Intro to XML

Intro to XML

Elliotte Rusty Harold

Software Development 2002 East

Monday, April 22, 2001

elharo@metalab.unc.edu

http://www.cafeconleche.org/

Outline

• Part I: XML Basics

• Part II: Well-formedness, DTDs and Validity

• Part III: Namespaces

• Part IV: XSL Transformations

• Part V: XML and Databases

• Part V: XML Processing APIs

Part I: XML Basics

XML succeeded, and in ways that weren't expected - at least not by many. Originally it was conceived as a document-oriented technology for robust quality publishing of documents over networks. the original workplan had three pillars - XML syntax, XML link, and XML stylesheets. Schemas were not high on the agenda and XML was not seen as an infrastructure for middleware or glueware. It was expected that at some stage it would be necessary to manage data but there was little activity in this area in 1997. When developing Chemical Markup Language (which must be one of the first published XML applications), I found the lack of datatypes very frustrating!

Well, XML is now a basic infrastructure of much modern information. I doubt that anyone now designs a protocol, or operating system without including XML. Although this list sometimes complains that XML isn't as clean as we would like, it works, and it works pretty well.

--Peter Murray-Rust on the xml-dev mailing list, Thursday, 07 Feb 2002

What is XML?

• Extensible Markup Language

• A syntax for documents

• A Meta-Markup Language

• A Structural and Semantic language, not a formatting language

• Not just for Web pages

Extensible Markup Language

Language

• It has a grammar

• It has a vocabulary (sort of)

• It can be parsed by machines

Markup Language

• It says what things are; not what they do

• It is not a programming language

• It is not compiled

Extensible

• You can add words to the language

XML is a Meta Markup Language

• Not like HTML, troff, LaTeX

• Make up the tags you need as you need them

• The tags you create can be documented in a Document Type Definition (DTD)

• A meta syntax for domain-specific markup languages like MusicML, MathML, and XHTML

XML Applications

• A specific markup language that uses the XML meta-syntax is called an XML application

• Different XML applications have their own more constricted syntaxes and vocabularies within the broader XML syntax

• Further syntax can be layered on top of this; e.g. data typing through schemas

Some XML Applications

• Human Resources Markup Language

• XML Court Interface

• Clinical Trial Data Model for drug trials

• National Library of Medicine (NLM) XML Data Formats for MEDLINE data over FTP replacing ELHILL Unit Record Format (EURF) on magnetic tape

• Health Level Seven XML Patient Record Architecture

• ASTM XML Document Type Definitions (DTDs) for Health Care

• Molecular Dynamics Markup Language (MoDL)

• BIOpolymer Markup Language (BIOML)

• Gene Expression Markup Language (GEML)

• Chemical Markup Language

• Bioinformatic Sequence Markup Language

• Open Financial Exchange

• and many more...

XML describes structure and semantics, not formatting

• XML documents form a tree

• Element and attribute names reflect the kind of the element

• Formatting can be added with a style sheet

A Song Description in HTML

<dt>Hot Cop
<dd> by Jacques Morali, Henri Belolo, and Victor Willis
<ul>
<li>Producer: Jacques Morali
<li>Publisher: PolyGram Records
<li>Length: 6:20
<li>Written: 1978
<li>Artist: Village People
</ul>

A Song Description in XML

<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>
</SONG>

Editing and Saving XML Files

• Plain ASCII or UTF-8 text

• .xml is customary file extension

• Any normal text editor will work

Style Sheets provide formatting

SONG {display: block; font-family: New York, Times New Roman, serif}
TITLE {display: block; font-size: 24pt; 
       font-weight: bold; font-family: Helvetica, sans}
COMPOSER {display: block}
PRODUCER {display: block}
YEAR {display: block}
PUBLISHER {display: block}
LENGTH {display: block}
ARTIST {display: block; font-style: italic}

Attaching style sheets to documents

• <?xml-stylesheet type="text/css" href="song1.css"?>

<?xml-stylesheet type="text/css" href="song.css"?>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>
</SONG>

Style Sheet Languages

• Cascading Style Sheets Level 1 (CSS1)

  • Internet Explorer 5.0 and later

  • Mozilla

  • Netscape 6

  • Opera 4.0, 5.0

• Cascading Style Sheets Level 2 (CSS2)

  • Internet Explorer 5.0 and later (partial)

  • Mozilla

  • Netscape 6

  • Opera 4.0, 5.0

• Extensible Stylesheet Language (XSL)

  • Mozilla 0.9.9

  • Internet Explorer 5.0/5.5 (older draft, buggy)

  • Internet Explorer 6.0

  • LotusXSL, Xalan, Saxon, other non-browser converters

• Document Style and Semantics Language (DSSSL)

  • Jade

An XSLT stylesheet

<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template match="/">
    <html>
      <head><title>Song</title></head>
      <body>
        <xsl:apply-templates select="SONG"/>    
      </body>
    </html>
  </xsl:template>
  
  <xsl:template match="SONG">
    <h1>
      <xsl:value-of select="TITLE"/> 
      by the 
      <xsl:value-of select="ARTIST"/>
    </h1>
    
    <ul>
      <li>Length: <xsl:value-of select="LENGTH"/></li>
      <li>Producer: <xsl:value-of select="PRODUCER"/></li>
      <li>Publisher: <xsl:value-of select="PUBLISHER"/></li>
      <li>Year: <xsl:value-of select="YEAR"/></li>
      <xsl:apply-templates select="COMPOSER"/>
    </ul>
  </xsl:template>

  <xsl:template match="COMPOSER">
    <li>Composer: <xsl:value-of select="."/></li>
  </xsl:template>

</xsl:stylesheet>

Transforming the Document

D:\fundamentals\examples>saxon hotcop.xml song3.xsl
<html>
   <head>
      <meta http-equiv="Content-Type" content="text/html; charset=utf-8">

      <title>Song</title>
   </head>
   <body>
      <h1>Hot Cop
         by the
         Village People
      </h1>
      <ul>
         <li>Length: 6:20</li>
         <li>Producer: Jacques Morali</li>
         <li>Publisher: PolyGram Records</li>
         <li>Year: 1978</li>
         <li>Composer: Jacques Morali</li>
         <li>Composer: Henri Belolo</li>
         <li>Composer: Victor Willis</li>
      </ul>
   </body>
</html>

Or alternately:

% java com.icl.saxon.StyleSheet hotcop.xml song3.xsl
<html>
...

CSS or XSL?

• CSS has broader support

• XSL is much more powerful

• XSL can be used without browser support by transforming to HTML on the server side

Well-formedness

Rules:

• Open and close all tags

• Empty-element tags end with />

• There is a unique root element

• Elements may not overlap

• Attribute values are quoted

• < and & are only used to start tags and entity references

• Only the five predefined entity references are used

• Plus more...

Validity

To be valid an XML document must be

1. Well-formed

2. Must have a Document Type Definition (DTD)

3. Must comply with the constraints specified in the DTD

A DTD for Songs

<!ELEMENT SONG (TITLE, COMPOSER+, PRODUCER*, PUBLISHER*, 
                 LENGTH?, YEAR?, ARTIST+)>

<!ELEMENT TITLE (#PCDATA)>

<!ELEMENT COMPOSER  (#PCDATA)>
<!ELEMENT PRODUCER  (#PCDATA)>
<!ELEMENT PUBLISHER (#PCDATA)>
<!ELEMENT LENGTH    (#PCDATA)>
<!-- This should be a four digit year like "1999",
     not a two-digit year like "99" -->
<!ELEMENT YEAR (#PCDATA)>

<!ELEMENT ARTIST (#PCDATA)>

A Valid Song Document

<!DOCTYPE SONG SYSTEM "song.dtd">
<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>
</SONG>

Checking Validity

To check validity you pass the document through a validating parser which should report any errors it finds. For example,

% java dom.Counter -v invalidhotcop.xml
[Error] invalidhotcop.xml:10:8: The content of element type "SONG" must match 
"(TITLE,COMPOSER+,PRODUCER*,PUBLISHER*,LENGTH?,YEAR?,ARTIST+)".
invalidhotcop.xml: 862;70;0 ms (7 elems, 0 attrs, 19 spaces, 59 chars)

A valid document:

% java dom.Counter -v validhotcop.xml
validhotcop.xml: 671;70;0 ms (10 elems, 0 attrs, 28 spaces, 98 chars)

A More Complex Example

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<?xml-stylesheet type="text/css" href="song.css"?>
<!DOCTYPE SONG SYSTEM "expanded_song.dtd">
<SONG xmlns="http://metalab.unc.edu/xml/namespace/song"
      xmlns:xlink="http://www.w3.org/1999/xlink">
  <TITLE>Hot Cop</TITLE>
  <PHOTO 
    xlink:type="simple" xlink:show="onLoad" xlink:href="hotcop.jpg"
    ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <!-- The publisher is actually Polygram but I needed 
       an example of a general entity reference. -->
  <PUBLISHER xlink:type="simple" xlink:href="http://www.amrecords.com/">
    A &amp; M Records
  </PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>
</SONG>
<!-- You can tell what album I was 
     listening to when I wrote this example -->

The XML Declaration

<?xml version="1.0" encoding="UTF-8" standalone="no"?>

• version attribute

  • required

  • always has the value 1.0

• standalone attribute

  • yes

  • no

• encoding attribute

  • UTF-8

  • ISO-8859-1

  • SJIS

  • etc.

Attributes

<PHOTO xlink:type="simple" xlink:show="onLoad" xlink:href="hotcop.jpg" ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200" />

• name="value" same as in HTML

• Generally used for meta-information

• Attribute values are quoted with either single or double quotes:

  • Good:

  • <A HREF="http://www.cafeconleche.org/">

  • <DIV ALIGN='CENTER'>

  • <A HREF="http://www.cafeconleche.org/">

  • <EMBED SRC="minnesotaswale.aif" hidden="true">

  • Bad:

  • <A HREF=http://www.cafeconleche.org/>

  • <DIV ALIGN=CENTER>

  • <EMBED SRC=minnesotaswale.aif hidden=true>

  • <EMBED SRC="minnesotaswale.aif" hidden>

Empty-element Tags

<PHOTO xlink:type="simple" xlink:show="onLoad" xlink:href="hotcop.jpg" ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200" />

• Ends with /> instead of >

• <PHOTO/> is semantically the same as <PHOTO></PHOTO>

• Just syntactic sugar

Comments

<!-- You can tell what album I was listening to when I wrote this example -->

• Essentially the same as in HTML

Namespaces

• Let you mix and match different XML vocabularies

• URIs identify elements and attributes that belong to different XML applications

• Prefixes can change if the URI stay the same

<SONG xmlns="http://www.cafeconleche.org/namespace/song"
      xmlns:xlink="http://www.w3.org/1999/xlink">
  <TITLE>Hot Cop</TITLE>
  <PHOTO 
    xlink:type="simple" xlink:show="onLoad" xlink:href="hotcop.jpg"
    ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>Jacques Morali</COMPOSER>
  <PUBLISHER xlink:type="simple" xlink:href="http://www.amrecords.com/">
    A &amp; M Records
  </PUBLISHER>
  <ARTIST>Village People</ARTIST>
</SONG>

Entity References

A & M Records

• < and & are only used to start tags and entities

  • Good:

    <H1>O'Reilly &amp; Associates</H1>

  • Bad:

    <H1>O'Reilly & Associates</H1>

  • Good:

    <CODE>for (int i = 0; i &lt;= args.length; i++ ) { </CODE>

  • Bad:

    <CODE>for (int i = 0; i <= args.length; i++ ) { </CODE>

• Only the five predefined entity references are used

  • Good:

    • &amp;

    • &lt;

    • &gt;

    • &quot;

    • &apos;

  • Bad:

    • &copy;

    • &reg;

    • &tm;

    • &alpha;

    • &eacute;

    • &nbsp;

    • etc.

• Entity references must end with a semicolon.

  • < is good

  • &lt is bad

A More Complex DTD

<!ELEMENT SONG (TITLE, PHOTO?, COMPOSER+, PRODUCER*, 
 PUBLISHER*, LENGTH?, YEAR?, ARTIST+)>
<!ATTLIST SONG xmlns       CDATA #REQUIRED
               xmlns:xlink CDATA #REQUIRED>
<!ELEMENT TITLE (#PCDATA)>

<!ELEMENT PHOTO EMPTY>
<!ATTLIST PHOTO xlink:type CDATA #FIXED "simple"
                xlink:href CDATA #REQUIRED
                xlink:show CDATA #IMPLIED
                ALT        CDATA #REQUIRED
                WIDTH      CDATA #REQUIRED
                HEIGHT     CDATA #REQUIRED
>

<!ELEMENT COMPOSER  (#PCDATA)>
<!ELEMENT PRODUCER  (#PCDATA)>
<!ELEMENT PUBLISHER (#PCDATA)>
<!ATTLIST PUBLISHER xlink:type CDATA #IMPLIED
                    xlink:href CDATA #IMPLIED
>

<!ELEMENT LENGTH (#PCDATA)>
<!-- This should be a four digit year like "1999",
     not a two-digit year like "99" -->
<!ELEMENT YEAR (#PCDATA)>

<!ELEMENT ARTIST (#PCDATA)>

What is XML used for?

• Domain-Specific Markup Languages

• Self-Describing Data

• Interchange of Data Among Applications

Domain-Specific Markup Languages

• Non proprietary format

• Don't pay for what you don't use

• You don't have to answer the questions you don't care about.

• Many free tools

• Huge support infrastructure

Self-Describing Data

• Much data is lost due to format problems

• XML is very simple

• XML is self-describing

• XML is well documented

An XML Fragment

<PERSON ID="p1100" SEX="M">
  <NAME>
    <GIVEN>Judson</GIVEN>
    <SURNAME>McDaniel</SURNAME>
  </NAME>
  <BIRTH>
    <DATE>21 Feb 1834</DATE>
  </BIRTH>
  <DEATH>
    <DATE>9 Dec 1905</DATE>
  </DEATH>
</PERSON>

Interchange of Data Among Applications

• E-commerce

• Syndication

• EAI and EDI

Example XML Applications

• Web Pages

• Mathematical Equations

• Music Notation

• Vector Graphics

• Metadata

• and more...

Mathematical Markup Language

<?xml version="1.0"?>
<!DOCTYPE html PUBLIC
  "-//W3C//DTD XHTML 1.1 plus MathML 2.0//EN"
  "http://www.w3.org/TR/MathML2/dtd/xhtml-math11-f.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:m="http://www.w3.org/1998/Math/MathML"
>
<head>
  <title>Fiat Lux</title>
</head>
<body>

<p>
And God said,
</p>

<m:math>
  <m:mrow>
    <m:msub>
      <m:mi>&delta;</m:mi>
      <m:mi>&alpha;</m:mi>
    </m:msub>
    <m:msup>
      <m:mi>F</m:mi>
      <m:mi>&alpha;&beta;</m:mi>
    </m:msup>
    <m:mi> </m:mi>
    <m:mo>=</m:mo>
    <m:mi></m:mi>
    <m:mfrac>
      <m:mrow>
        <m:mn>4</m:mn>
        <m:mi>&pi;</m:mi>
      </m:mrow>
      <m:mi>c</m:mi>
    </m:mfrac>
    <m:mi> </m:mi>
    <m:msup>
      <m:mi>J</m:mi>
      <m:mrow>
        <m:mi>&beta;</m:mi>
        <m:mo> </m:mo>
      </m:mrow>
    </m:msup>
  </m:mrow>
</m:math>

<p>
and there was light
</p>
</body>
</html>

Channel Definition Format

<?xml version="1.0"?>
<CHANNEL HREF="http://www.cafeconleche.org/index.html">
  <TITLE>Cafe con Leche</TITLE>
  <ITEM HREF="http://www.cafeconleche.org/books.html">
    <TITLE>Books about XML</TITLE>
  </ITEM>
  <ITEM HREF="http://www.cafeconleche.org/tradeshows.html">
    <TITLE>Trade shows and conferences about XML</TITLE>
  </ITEM>
  <ITEM HREF="http://www.cafeconleche.org/lists.htm">
    <TITLE>Mailing Lists dedicated to XML</TITLE>
  </ITEM>
</CHANNEL>

Classic Literature

• The Complete Plays of Shakespeare

• The Bible

• The Koran

• The Book of Mormon

• Joseph Conrad's Heart of Darkness

Vector Graphics

• Vector Markup Language (VML)

• Internet Explorer 5.0

• Microsoft Office 2000

• Scalable Vector Graphics (SVG)

The Resource Description Framework (RDF)

• Meta-data

• Dublin Core

• Better Web searching

An Example of RDF

<rdf:RDF 
 xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:dc="http://purl.org/DC/">
  <rdf:Description about="http://www.cafeconleche.org/">
    <dc:creator>Elliotte Rusty Harold</dc:creator>
    <dc:title>Cafe con Leche</dc:title>
  </rdf:Description>
</rdf:RDF>

File Formats, in-house applications, and other behind the scenes uses

• Microsoft Office 2000

• Netscape What's Related

XML for XML

• XSL: The Extensible Stylesheet Language

• XML Schema

• XLinks

• XInclude

XSL: The Extensible Stylesheet Language

• XSLT: XSL Transformations

• XSL-FO XSL Formatting Objects

An XML document

<?xml version="1.0"?>
<PERIODIC_TABLE>

  <ATOM STATE="GAS">
    <NAME>Hydrogen</NAME>
    <SYMBOL>H</SYMBOL>
    <ATOMIC_NUMBER>1</ATOMIC_NUMBER>
    <ATOMIC_WEIGHT>1.00794</ATOMIC_WEIGHT>
    <BOILING_POINT UNITS="Kelvin">20.28</BOILING_POINT>
    <MELTING_POINT UNITS="Kelvin">13.81</MELTING_POINT>
    <DENSITY UNITS="grams/cubic centimeter">
      <!-- At 300K, 1 atm -->
      0.0000899
    </DENSITY>
  </ATOM>

  <ATOM STATE="GAS">
    <NAME>Helium</NAME>
    <SYMBOL>He</SYMBOL>
    <ATOMIC_NUMBER>2</ATOMIC_NUMBER>
    <ATOMIC_WEIGHT>4.0026</ATOMIC_WEIGHT>
    <BOILING_POINT UNITS="Kelvin">4.216</BOILING_POINT>
    <MELTING_POINT UNITS="Kelvin">0.95</MELTING_POINT>
    <DENSITY UNITS="grams/cubic centimeter"><!-- At 300K -->
      0.0001785
    </DENSITY>
  </ATOM>

</PERIODIC_TABLE>

An XSLT style sheet that converts to XSL-FO

<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:fo="http://www.w3.org/1999/XSL/Format">

  <xsl:output indent="yes"/>

  <xsl:template match="/">
    <fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">

      <fo:layout-master-set>
        <fo:simple-page-master master-name="only">
          <fo:region-body/>
        </fo:simple-page-master>
      </fo:layout-master-set>

      <fo:page-sequence master-reference="only">

        <fo:flow flow-name="xsl-region-body">
          <xsl:apply-templates select="//ATOM"/>
        </fo:flow>

      </fo:page-sequence>

    </fo:root>
  </xsl:template>

  <xsl:template match="ATOM">
    <fo:block font-size="20pt" font-family="serif"
              line-height="30pt">
      <xsl:value-of select="NAME"/>
    </fo:block>
  </xsl:template>

</xsl:stylesheet>

The XSL-FO Output

<?xml version="1.0" encoding="utf-8"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
   <fo:layout-master-set>
      <fo:simple-page-master master-name="only">
         <fo:region-body/>
      </fo:simple-page-master>
   </fo:layout-master-set>
   <fo:page-sequence master-reference="only">
      <fo:flow flow-name="xsl-region-body">
         <fo:block font-size="20pt" font-family="serif" line-height="30pt">Hydrogen</fo:block>
         <fo:block font-size="20pt" font-family="serif" line-height="30pt">Helium</fo:block>
      </fo:flow>
   </fo:page-sequence>
</fo:root>

W3C XML Schemas

• An XML syntax that provides an alternative to DTD validation

• Data typing of element and attribute content

---

<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <xsd:element name="SONG" type="SongType"/>

  <xsd:complexType name="SongType">
    <xsd:sequence>
      <xsd:element name="TITLE"     type="xsd:string"
                   minOccurs="1"    maxOccurs="1"/>
      <xsd:element name="COMPOSER"  type="xsd:string"
                   minOccurs="1"    maxOccurs="unbounded"/>
      <xsd:element name="PRODUCER"  type="xsd:string"
                   minOccurs="0"    maxOccurs="unbounded"/>
      <xsd:element name="PUBLISHER" type="xsd:string"
                   minOccurs="0"    maxOccurs="1"/>
      <xsd:element name="LENGTH"    type="xsd:string"
                   minOccurs="1"    maxOccurs="1"/>
      <xsd:element name="YEAR"      type="xsd:gYear"
                   minOccurs="1"    maxOccurs="1"/>
      <xsd:element name="ARTIST"    type="xsd:string"
                   minOccurs="1"    maxOccurs="unbounded"/>
      <xsd:element name="PRICE"     type="xsd:string"
                   minOccurs="0"    maxOccurs="1"/>
    </xsd:sequence>
  </xsd:complexType>

</xsd:schema>

---

XML Hypertext

Linking in XML is divided into multiple parts:

• A Uniform Resource Identifier (URI) names or locates a resource

• An XLink defines connections between two or more documents identified by URIs

• XPath identifies particular nodes within a document

• An XPointer adds an XPath to a URI

• XBase defines the URI against which relative URIs are resolved

• XInclude embeds a document identified by a URI inside an XML document.

XML Hypertext Example

<?xml version="1.0"?>
<story date="January 9, 2001"
       xmlns:xlink="http://www.w3.org/1999/xlink"
       xmlns:xi="http://www.w3.org/2001/XInclude"
       xml:base="http://www.cafeaulait.org/">

  <p>
    The W3C XML Linking Working Group has pushed the 
    <cite xlink:href="http://www.w3.org/TR/2001/WD-xptr-20010108">
      XPointer specification
    </cite> 
    back to working draft status. The specific issue that was 
    uncovered during Candidate Recommendation was some 
    <em xlink:type="simple"
      xlink:href="http://www.w3.org/TR/xptr#xpointer(//div[@class='div3'][7])">
      confusion
    </em> 
    over how to integrate XPointers, particularly those  
   in non-XML documents, with namespaces. 
   </p>

   <p>
     It's also come to light in this draft that Sun has 
     <em xlink:type="simple"
      xlink:href=
      "http://lists.w3.org/Archives/Public/www-xml-linking-comments/2000OctDec/0092.html"
      >
      claimed a patent</em> on some of the technologies needed to 
      implement XPointer. I think this is particularly offensive 
      because Eve L. Maler, a Sun employee, served as co-chair of 
      the XML Linking Working Group and a co-editor of the XPointer 
      specification. As usual Sun wants to use this as a club to lock 
      implementers and users into a licensing agreement that goes 
      beyond what Sun and the W3C could otherwise demand. The specific 
      patent is <cite>United States Patent No. 5,659,729, Method and 
      system for implementing hypertext scroll attributes</cite>, issued 
      to Jakob Nielsen in 1997. The patent was filed on February 1, 1996. 
      It claims:
  </p>
  <blockquote>
    <xi:include href=
      "http://www.delphion.com/details?&pn=US05659729__#xpointer(//abstract)"
    ></xi:include>
  </blockquote>
  
</story>

XLinks

• Any element can be a link

• Links can be bi-directional

• Links can even be multi-directional

• Links can be separated from the documents they connect

<footnote xlink:type="simple" xlink:href="footnote7.xml">7</footnote>

Extended Links

• Simple links are very similar to HTML links, one-directional, one-element-to-one-document links

• Extended links are multi-directional, many-to-many links

• An extended link is a list of nodes and a list of the connections between them

Extended Link Example

<WEBSITE xmlns:xlink="http://www.w3.org/1999/xlink"
         xlink:type="extended" xlink:title="Cafe au Lait">

  <NAME xlink:type="resource" xlink:label="source">
    Cafe au Lait
  </NAME>

  <HOMESITE xlink:type="locator"
           xlink:href="http://www.cafeaulait.org/"
           xlink:label="ny"/>

  <MIRROR xlink:type="locator"
         xlink:title="Cafe au Lait Swedish Mirror"
         xlink:label="se"
         xlink:href="http://sunsite.kth.se/javafaq"/>

  <MIRROR xlink:type="locator"
         xlink:title="Cafe au Lait U.S. Mirror"
         xlink:label="nc"
         xlink:href="http://ibiblio.org/javafaq/"/>

  <MIRROR xlink:type="locator"
         xlink:title="Cafe au Lait Swiss Mirror"
         xlink:label="ch"
         xlink:href="http://sunsite.cnlab-switch.ch/javafaq"/>

  <CONNECTION xlink:type="arc" xlink:from="source"
              xlink:to="ch"    xlink:show="replace"
              xlink:actuate="onRequest"/>
  <CONNECTION xlink:type="arc" xlink:from="source"
              xlink:to="ny"    xlink:show="replace"
              xlink:actuate="onRequest"/>
  <CONNECTION xlink:type="arc" xlink:from="source"
              xlink:to="se"    xlink:show="replace"
              xlink:actuate="onRequest"/>
  <CONNECTION xlink:type="arc" xlink:from="source"
              xlink:to="nc"    xlink:show="replace"
              xlink:actuate="onRequest"/>

</WEBSITE>

Diagram of an Extended Link

XInclude

• A means of merging multiple XML document or parts thereof

• Not yet finished

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE book SYSTEM "book.dtd" >
<book xmlns:xinclude="http://www.w3.org/2001/XInclude">
  <title>The Java Developer's Resource</title>
  <last_modified>December 3, 2000</last_modified>
    
  <xinclude:include href="getting_started.xml"/>
  <xinclude:include href="procedural_java.xml"/>
  
</book>

Non-XML for XML

• XPath, the XML Path Language

• XPointers

• MathML and XSL-FO are intended as an output format only. Other languages will be written and then transformed into these formats.

• DTDs are only technically XML

XPath

• A syntax for addressing into an XML document

• Used in XPointer and XSLT

• Basis for XML Query Language

descendant::language[position()=2]
/child::spec/child::body/child::*/child::language[2]
/spec/body/*/language[2]

XPointers

• A syntax for addressing into an XML document

• Extend XPath to support non-well-formed points and ranges

• Used by XLink and XInclude

xpointer(id("ebnf"))
xpointer(descendant::language[position()=2])
ebnf
xpointer(/child::spec/child::body/child::*/child::language[2])
xpointer(/spec/body/*/language[2])
/1/14/2
xpointer(id("ebnf"))xpointer(id("EBNF"))

XPointers and URIs

• XPointers are normally attached to the end of URIs as fragment identifiers

• This is how they're used by XLink and XInclude

http://www.w3.org/TR/1998/REC-xml-19980210.xml#xpointer(id("ebnf"))
http://www.w3.org/TR/1998/REC-xml-19980210.xml#xpointer(descendant::language[position()=2])
http://www.w3.org/TR/1998/REC-xml-19980210.xml#ebnf
http://www.w3.org/TR/1998/REC-xml-19980210.xml#xpointer(/child::spec/child::body/child::*/child::language[2])
http://www.w3.org/TR/1998/REC-xml-19980210.xml#xpointer(/spec/body/*/language[2])
http://www.w3.org/TR/1998/REC-xml-19980210.xml#/1/14/2
http://www.w3.org/TR/1998/REC-xml-19980210.xml#xpointer(id("ebnf"))xpointer(id("EBNF"))

A larger example: Music Catalog

• Examine the data

• Design a vocabulary for the data

• Write a style sheet

Sample Catalog

Organizing the Data

• XML documents are trees.

• XML elements contain other elements as well as text

• Within these limits there's more than one way to organize the data

  • Hierarchically

  • Relationally

  • Objects

What is the Root Element

• The catalog?

• A custom Document element?

The Root Element

• Choose catalog for the root element

• Everything else will be a descendant of catalog

• This is not the only possible choice

<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>
  Everything else will go here...
</catalog>

What are the Immediate Children of the Root?

• Composers?

• Songs/Compositions?

• Categories?

• All of the Above?

Child Elements

<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>

  <category>
    Small chamber ensembles - 2-4 Players by New York Women Composers
  </category>

</catalog>

White space in XML is not especially significant

<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog><category>Small chamber ensembles 
- 2-4 Players by New York Women Composers</category></catalog>

Composers

Each composer has a name

<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>

  <category>
    Small chamber ensembles - 2-4 Players by New York Women Composers
  </category>

  <composer>
    <name>Julie Mandel</name>
  </composer>

  <composer>
    <name>Margaret De Wys</name>
  </composer>  
    
  <composer>
    <name>Beth Anderson</name>
  </composer>
    
  <composer>
    <name>Linda Bouchard</name>
  </composer>

</catalog>

Grand Children

• It's better for sorting to divide names into first, middle, and last

• Some (e.g. middle name) elements may be empty

<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>

  <category>
    Small chamber ensembles - 2-4 Players by New York Women Composers
  </category>

  <composer>
    <name>
      <first_name>Julie</first_name> 
      <middle_name></middle_name> 
      <last_name>Mandel</last_name>
    </name>
  </composer>

  <composer>
    <name>
      <first_name>Margaret</first_name> 
      <middle_name>De</middle_name> 
      <last_name>Wys</last_name>
    </name>
  </composer>  
    
  <composer>
    <name>
      <first_name>Beth</first_name> 
      <middle_name></middle_name> 
      <last_name>Anderson</last_name>
    </name>
  </composer>
    
  <composer>
    <name>
      <first_name>Linda</first_name> 
      <middle_name></middle_name> 
      <last_name>Bouchard</last_name>
    </name>
  </composer>

</catalog>

Attributes

• Some people have the same names

• Use an ID number to disambiguate

• Store the ID number in an id attribute

• name=value

• An element may not have two attributes with the same name

• Attribute values must be quoted

<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>

  <category>
    Small chamber ensembles - 2-4 Players by New York Women Composers
  </category>

  <composer id="c1">
    <name>
      <first_name>Julie</first_name> 
      <middle_name></middle_name> 
      <last_name>Mandel</last_name>
    </name>
  </composer>

  <composer id="c2">
    <name>
      <first_name>Margaret</first_name> 
      <middle_name>De</middle_name> 
      <last_name>Wys</last_name>
    </name>
  </composer>  
    
  <composer id="c3">
    <name>
      <first_name>Beth</first_name> 
      <middle_name></middle_name> 
      <last_name>Anderson</last_name>
    </name>
  </composer>
    
  <composer id="c4">
    <name>
      <first_name>Linda</first_name> 
      <middle_name></middle_name> 
      <last_name>Bouchard</last_name>
    </name>
  </composer>

</catalog>

Attributes vs. Elements

• Attribute are for meta-data; elements are for data.

• Does the reader want to see the information? If yes, use element content; if no, use attributes

• Attributes are good for ID numbers, URLs, references, and other information not directly relevant to the reader

When not to use attributes

• Attributes can't hold structure well.

• Elements allow you to include meta-meta-data (information about the information about the information).

• Not everyone always agrees on what is and isn't meta-data.

• Elements are more extensible in the face of future changes.

Compositions

Let's look at an example of what we want:

Rendered HTML:

Brass Swale (1988) 5", tbn, 2 Bfl tpts, bar. hn

Tonal. Commissioned/Premiered by the Redlands' New Music Ensemble. (A swale is a meadow or a marsh where a lot of wild plants grow together. The composer discovered the word when a horse named Swale won the Kentucky Derby several years ago. Since her work is primarily collage of newly composed musical swatches, she has used the name extensively.) ACA - American Composers Alliance

Or in HTML:

<dt><cite>Brass Swale</cite> (1988) 5", tbn, 2 Bfl tpts, bar. hn</dt>
<dd><p>
Tonal. Commissioned/Premiered by the Redlands' New Music 
Ensemble. (A swale is a meadow or a marsh where a lot of 
wild plants grow together. The composer discovered the word 
when a horse named Swale won the Kentucky Derby several 
years ago. Since her work is primarily collage of newly 
composed musical swatches, she has used the name 
extensively.)  ACA - American Composers 
Alliance</p>
</dd>

Each composition has a

• Title

• Date

• Description

• List of instruments

• Length

• Publisher

• Some pieces may be missing from some compositions

Composition Example in XML

  <composition>
    <title>Brass Swale</title>
    <date>1988</date> 
    <length>5"</length>
    <instruments>tbn, 2 Bfl tpts, bar, hn</instruments>
    <description>
      Tonal. Commissioned/Premiered by the Redlands' New Music
      Ensemble. (A swale is a meadow or a marsh where a lot of
      wild plants grow together. The composer discovered the word
      when a horse named Swale won the Kentucky Derby several
      years ago. Since her work is primarily collage of newly
      composed musical swatches, she has used the name
      extensively.)
    </description>
    <publisher>ACA - American Composers Alliance</publisher>
  </composition>

Further Divisions

  <composition>
    <title>Trio for Flute, Viola and Harp</title>
    <date><year>1994</year></date> 
    <length>13'38"</length>
    <instruments>fl, hp, vla</instruments>
    <description>
      <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
      Christine Ims, and Susan Jolles. In 3 movements :</p>
      <ul>
        <li>mvt. 1: 5:01</li>
        <li>mvt. 2: 4:11</li>
        <li>mvt. 3: 4:26</li>
      </ul>  
    </description>
    <publisher>Theodore Presser</publisher>
  </composition>

Attaching the Composer to the Composition

  <composition composer="c3">
    <title>Trio: Dream in D</title>
    <date><year>1980</year></date> 
    <length>10'</length>
    <instruments>fl, pn, vc, or vn, pn, vc</instruments>
    <description>
      Rhapsodic. Passionate. Available on CD 
      <cite><a href=
       "http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr%3D1-2/">
       Two by Three
      </a></cite> from North/South Consonance (1998).
    </description> 
    <publisher></publisher>
  </composition>

Some Keywords For the Search Engines

<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>

  <category>
    Small chamber ensembles - 2-4 Players by New York Women Composers
  </category>

  <cataloging_info>
    <abstract>Compositions by the members of New York Women Composers</abstract>
    <keyword>music publishing</keyword>
    <keyword>scores</keyword>
    <keyword>women composers</keyword>
    <keyword>New York</keyword>
  </cataloging_info>

  <composer id="c1">
    <name>
      <first_name>Julie</first_name> 
      <middle_name></middle_name> 
      <last_name>Mandel</last_name>
    </name>
  </composer>
  
  ...
  
</catalog>

Standard Signature

• Copyright notice

• Name of maintainer

• Email address of maintainer

• Last modified date

<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>
...
  <last_updated>July 28, 1999</last_updated>
  <copyright>1999 New York Women Composers</copyright>
  <maintainer email="elharo@metalab.unc.edu" 
              url="http://www.elharo.com/">
    <name>
      <first_name>Elliotte</first_name> 
      <middle_name>Rusty</middle_name> 
      <last_name>Harold</last_name>
    </name>
  </maintainer>

</catalog>

Cascading Style Sheets

• Partially supported by Mozilla, IE 5.0, and Opera 4.0

• Full W3C Recommendation

A Blank Style Sheet

<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml-stylesheet type="text/css" href="compositions1.css"?>
<catalog>
...
</catalog>

The Default Rule

• Not every element needs a rule

• The root element should be at least display: block

catalog { font-family: "New York", "Times New Roman", serif; 
          font-size: 14pt; 
          background-color: white; 
          color: black; 
          display: block }

A style rule for the category element

• Make it look like an H1 heading

category { display: block; 
          font-family: Helvetica, Arial, sans;
          font-size: 32pt; 
          font-weight: bold; 
          text-align: center
         }
       
catalog { font-family: New York, Times New Roman, serif; 
          font-size: 14pt; 
          background-color: white; 
          color: black; 
          display: block 
        }

A style rule for the composer element

• Make it look like a level 2 head

• No need to stylize the first, middle, and last names separately

composer { display: block; 
          font-family: Helvetica, Arial, sans;
          font-size: 24pt; 
          font-weight: bold; 
          text-align: left
         }     

A style rule for the title element

composition title { display: block; 
       font-family: Helvetica, Arial, sans;
       font-size: 18pt; 
       font-weight: bold; 
       text-align: left
      }                

A style rule for the catalog info

// cataloging_info is only for search engines
cataloging_info { display: none;
       color: white}                

display: none requires CSS2:

Style rules for the signature

  <last_updated>July 28, 1999</last_updated>
  <copyright>1999 New York Women Composers</copyright>
  <maintainer email="elharo@metalab.unc.edu" 
              url="http://www.elharo.com/">
    <name>
      <first_name>Elliotte</first_name> 
      <middle_name>Rusty</middle_name> 
      <last_name>Harold</last_name>
    </name>
  </maintainer>            

last_updated, copyright, maintainer {display: block;
       font-size: small}
       
copyright:before {content: "Copyright " }

last_updated:before {content: "Last Modified " }

last_updated {margin-top: 2ex }

Again, some of this requires CSS2

Style Rules for composition children

composition * {display:list-item}
       
description {display: block}

Finished Style Sheet

category { display: block; 
          font-family: Helvetica, Arial, sans;
          font-size: 32pt; 
          font-weight: bold; 
          text-align: center
         }
       
catalog { font-family: "New York", "Times New Roman", serif; 
          font-size: 14pt; 
          background-color: white; 
          color: black; 
          display: block
        }
      
composer { display: block; 
           font-family: Helvetica, Arial, sans;
           font-size: 24pt; 
           font-weight: bold; 
           text-align: left
         }  
       
composition title { display: block; 
       font-family: Helvetica, Arial, sans;
       font-size: 18pt; 
       font-weight: bold; 
       text-align: left}
       
composition * {display:list-item}
       
description {display: block}
              
// cataloging_info is only for search engines
cataloging_info { display: none;
       color: #FFFFFF}
       
last_updated, copyright, maintainer {display: block;
       font-size: small}
       
copyright:before {content: "Copyright " }

last_updated:before {content: "Last Modified " }

last_updated {margin-top: 2ex }

Possible Extensions

• Should be able to match composers with compositions

• Should be able to sort composers and compositions by name

• Should be able to include data from attributes; e.g. the maintainer's email address

• Horizontal rules would be nice

• Better header (e.g. title and meta tags) would be nice

Possible Solutions

• CSS Level 3?

• XSL

• XSL + JavaScript

CSS or XSL?

• CSS has broader support

• CSS is more stable

• XSL is much more powerful

• XSL can be used without browser support by transforming to HTML on the server side

Part II: Well-formedness, DTDs, and Validity

The great innovation of SGML was requiring documents to define their own type. The great innovation of XML was to remove this requirement.

--Joe English on the xml-dev mailing list, Tue, 26 Mar 2002

Well-formedness vs validity

• There are two levels of conformance to XML

• Well-formed documents are correct with or without a DTD. They adhere to the basic syntax rules of XML

• Valid documents also adhere to the constraints specified in a DTD

• All valid documents are well-formed; not all well-formed document are valid.

Well-formedness Rules

• Open and close all tags

• Empty-element tags end with />

• There is a unique root element

• Elements may not overlap

• Attribute values are quoted

• < and & are only used to start tags and entity references

• Only the five predefined entity references are used

• Plus more...

Open and close all tags

• Good:

  • <p>The quick brown fox jumped over the lazy dog</p>

  • <li>A very <B>important</B> point</li>

  • Copyright 1999 Elliotte Rusty Harold<br></br>

• Bad:

  • The quick brown fox jumped over the lazy dog<p>

  • <li>A very <B>important point

  • Copyright 1999 Elliotte Rusty Harold<br>

Empty-element tags end with />

• <BR/>, <HR/>, and <IMG/> instead of <BR>, <HR>, and <IMG>

• Web browsers deal inconsistently with these

• Can use <BR></BR> <HR></HR> <IMG></IMG> instead

• <BR CLASS="EMPTY"/> seems to work best.

There is a unique root element

• One element completely contains all other elements of the document

• This is HTML in HTML files

• The XML declaration and xml-stylesheet processing instruction are not elements

Elements may not overlap

• If an element contains a start tag for an element, it must also contain the corresponding end tag

• Empty elements may appear anywhere

• Every non root element has a parent element

Attribute values are quoted

• Good:

• <A HREF="http://www.cafeconleche.org/">

• <DIV ALIGN="CENTER">

• <A HREF="http://www.cafeconleche.org/">

• <EMBED SRC="minnesotaswale.aif" hidden="hidden">

• Bad:

• <A HREF=http://www.cafeconleche.org/>

• <DIV ALIGN=CENTER>

• <EMBED SRC=minnesotaswale.aif hidden=hidden>

• <EMBED SRC="minnesotaswale.aif" hidden>

< and & are only used to start tags and entities

• Good:

  
  <H1>O'Reilly &amp; Associates</H1>
  

• Bad:

  
  <H1>O'Reilly & Associates</H1>
  

• Good:

  <CODE>for (int i = 0; i &lt;= args.length; i++ ) { </CODE>
  

• Bad:

  <CODE>for (int i = 0; i <= args.length; i++ ) { </CODE>
  

Only the five predefined entity references are used

• Good:

• &amp;

• &lt;

• &gt;

• &quot;

• &apos;

• Bad:

• &copy;

• &reg;

• &tm;

• &alpha;

• &eacute;

• &nbsp;

• etc.

• Entity references must end with a semicolon.

  • < is good

  • &lt is bad

Character References

• Decimal:

  ¡	¡
  ¢	¢
  £	£
  ¤	¤
  ¥	¥
  ¦	¦
  etc. for all other Unicode values that are allowed in XML documents

• Hexadecimal

  ¡	¡
  ¢	¢
  £	£
  ¤	¤
  ¥	¥
  ¦	¦
  etc. for all other Unicode values that are allowed in XML documents

XML is a Meta Markup Language

• Not like HTML, troff, LaTeX

• Make up the tags you need as you need them

• The tags you create can be documented in a Document Type Definition (DTD)

• A meta syntax for domain-specific markup languages like MusicML, MathML, and CML

A Song Description in XML

<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>
</SONG>

A DTD for Songs

<!ELEMENT SONG (TITLE, COMPOSER+, PRODUCER*, PUBLISHER*, 
                 LENGTH?, YEAR?, ARTIST+)>

<!ELEMENT TITLE (#PCDATA)>

<!ELEMENT COMPOSER  (#PCDATA)>
<!ELEMENT PRODUCER  (#PCDATA)>
<!ELEMENT PUBLISHER (#PCDATA)>
<!ELEMENT LENGTH    (#PCDATA)>
<!-- This should be a four digit year like "1999",
     not a two-digit year like "99" -->
<!ELEMENT YEAR (#PCDATA)>

<!ELEMENT ARTIST (#PCDATA)>

A Valid Song Document

<!DOCTYPE SONG SYSTEM "song.dtd">
<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>
</SONG>

Validity

To be valid an XML document must be

1. Well-formed

2. Must have a document type declaration

3. Must comply with the constraints specified in the DTD

Checking Validity

To check validity you pass the document through a validating parser which should report any errors it finds. For example,

% java sax.Counter -v invalidhotcop.xml
Error at (file file:/D:/speaking/SD99EAST/dtds/invalidhotcop.xml, line 10, char
8): Element "<SONG>" is not valid because it does not follow the rule, "(TITLE,C
OMPOSER+,PRODUCER*,PUBLISHER*,LENGTH?,YEAR?,ARTIST+)".
invalidhotcop.xml: 281 ms

A valid document:

% java sax.Counter -v validhotcop.xml
validhotcop.xml: 170 ms

Internal DTDs

<?xml version="1.0"?>
<!DOCTYPE SONG [
  <!ELEMENT SONG (TITLE, COMPOSER+, PRODUCER*, PUBLISHER*, 
                  LENGTH?, YEAR?, ARTIST+)>

  <!ELEMENT TITLE     (#PCDATA)>
  <!ELEMENT COMPOSER  (#PCDATA)>
  <!ELEMENT PRODUCER  (#PCDATA)>
  <!ELEMENT PUBLISHER (#PCDATA)>
  <!ELEMENT LENGTH    (#PCDATA)>
  
  <!-- This should be a four digit year like "1999",
     not a two-digit year like "99" -->
  <!ELEMENT YEAR   (#PCDATA)>
  <!ELEMENT ARTIST (#PCDATA)>
]>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>
</SONG>

What is XML used for?

• Domain-Specific Markup Languages

• Self-Describing Data

• Interchange of Data Among Applications

Domain-Specific Markup Languages

• A DTD precisely describes the format

• DTDs verify that documents adhere to the format

• Ensures interoperability of unrelated tools

Self-Describing Data

• DTDs explain the format so reverse engineering isn't as necessary

• Comments in DTDs can go even further

<!-- This should be a four digit year like "1999",
     not a two-digit year like "99" -->
<!ELEMENT YEAR (#PCDATA)>

Interchange of Data Among Applications

• E-commerce and syndication

• DTDs make sure that two independent applications speak the same language

• DTDs detect malformed data

• DTDs verify correct data

XML Applications

• A specific markup language that uses the XML meta-syntax is called an XML application

• Different XML applications have their own more constricted syntaxes and vocabularies within the broader XML syntax

• The DTD documents this syntax

• Further syntax can be layered on top of this; e.g. data typing through schemas

DTDs and Validity

• A Document Type Definition describes the elements and attributes that may appear in a document

• Validation compares a particular document against a DTD

• Well-formedness is a prerequisite for validity

What is a DTD?

• A DTD lists the elements, attributes, and entities contained in a document

• A DTD defines the relationships between different elements and attributes

• internal vs. external DTDs

The importance of validation

• Ensures that data is correct before feeding it into a program

• Ensures that a format is followed

• Establishes what must be supported

• Not all documents need to be valid; sometimes well-formed is enough

An Example Document

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE catalog SYSTEM "compositions.dtd">
<catalog>

  <category>
    Small chamber ensembles - 2-4 Players by New York Women Composers
  </category>

  <cataloging_info>
    <abstract>Compositions by the members of New York Women Composers</abstract>
    <keyword>music publishing</keyword>
    <keyword>scores</keyword>
    <keyword>women composers</keyword>
    <keyword>New York</keyword>
  </cataloging_info>

  <last_updated>July 28, 1999</last_updated>
  <copyright>1999 New York Women Composers</copyright>
  <maintainer email="elharo@metalab.unc.edu" 
              url="http://www.elharo.com/">
    <name>
      <first_name>Elliotte</first_name> 
      <middle_name>Rusty</middle_name> 
      <last_name>Harold</last_name>
    </name>
  </maintainer>

  <composer id="c1">
    <name>
      <first_name>Julie</first_name> 
      <middle_name></middle_name> 
      <last_name>Mandel</last_name>
    </name>
  </composer>

  <composer id="c2">
    <name>
      <first_name>Margaret</first_name> 
      <middle_name>De</middle_name> 
      <last_name>Wys</last_name>
    </name>
  </composer>  
    
  <composer id="c3">
    <name>
      <first_name>Beth</first_name> 
      <middle_name></middle_name> 
      <last_name>Anderson</last_name>
    </name>
  </composer>
    
  <composer id="c4">
    <name>
      <first_name>Linda</first_name> 
      <middle_name></middle_name> 
      <last_name>Bouchard</last_name>
    </name>
  </composer>
    
  <composition composer="c1">
    <title>Trio for Flute, Viola and Harp</title>
    <date><year>1994</year></date> 
    <length>13'38"</length>
    <instruments>fl, hp, vla</instruments>
    <description>
      <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
      Christine Ims, and Susan Jolles. In 3 movements :</p>
      <ul>
        <li>mvt. 1: 5:01</li>
        <li>mvt. 2: 4:11</li>
        <li>mvt. 3: 4:26</li>
      </ul>  
    </description>
    <publisher>Theodore Presser</publisher>
  </composition>

  <composition composer="c2">
    <title>Charmonium</title>
    <date><year>1991</year></date> 
    <length>9'</length>
    <instruments>2 vln, vla, vc</instruments>
    <description>
      <p>Commissioned as quartet for the Meridian String Quartet. 
      Sonorous, bold. Moderate difficulty. Tape available.</p>
    </description> 
  </composition>

  <composition composer="c1">
    <title>Invention for Flute and Piano</title>
    <date><year>1994</year></date> 
    <instruments>fl, pn</instruments>
    <description><p>3 movements</p></description> 
  </composition>

  <composition composer="c3">
    <title>Little Trio</title>
    <date><year>1984</year></date> 
    <length>4'</length>
    <instruments>fl, guit, va</instruments>
    <publisher>ACA</publisher>
  </composition>

  <composition composer="c3">
    <title>Dr. Blood's Mermaid Lullaby</title>
    <date><year>1980</year></date> 
    <length>3'</length>
    <instruments>fl or ob, or vn, or vc, pn</instruments>
    <publisher>ACA</publisher>
  </composition>

  <composition composer="c3">
    <title>Trio: Dream in D</title>
    <date><year>1980</year></date> 
    <length>10'</length>
    <instruments>fl, pn, vc, or vn, pn, vc</instruments>
    <description>
      <p>Rhapsodic. Passionate. Available on CD 
      <cite>
      <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/">
      Two by Three</a></cite> 
      from North/South Consonance (1998).</p>
    </description> 
  </composition>

  <composition composer="c4">
    <title>Propos II</title>
    <date><year>1985</year></date> 
    <length>11'</length>
    <instruments>2 tpt</instruments>
    <description><p>Arrangement from Propos</p></description> 
  </composition>

  <composition composer="c4">
    <title>Rictus En Mirroir</title>
    <date><year>1985</year></date> 
    <length>14'</length>
    <instruments>fl, ob, hpschd, vc</instruments>
  </composition>

</catalog>

Element Declarations

• Each tag must be declared in a <!ELEMENT> declaration.

• A <!ELEMENT> declaration gives the name and content specification of the element

• The content specification uses a simple regular expression-like grammar to precisely specify what is and isn't allowed in an element

Content Specifications

• ANY

• #PCDATA

• Sequences

• Choices

• Mixed Content

• Modifiers

• EMPTY

ANY

<!ELEMENT catalog ANY>

• A catalog can contain any child element and/or raw text (parsed character data)

#PCDATA

• Parsed Character Data; i.e. raw text, no markup. For example,

  <year>1984</year>

<!ELEMENT year (#PCDATA)>

#PCDATA

• Valid:

<year>1999</year>
<year>99</year>
<year>1999 C.E.</year>
<year>
 The year of our Lord one thousand, nine hundred, and ninety-nine
</year>

• Invalid:

<year>
<month>January</month>
<month>February</month>
<month>March</month>
<month>April</month>
<month>May</month>
<month>June</month>
<month>July</month>
<month>August</month>
<month>September</month>
<month>October</month>
<month>November</month>
<month>December</month>
</year>

#PCDATA

There are a number of elements in the example document that only contain PCDATA:

<!ELEMENT category     (#PCDATA)>
<!ELEMENT abstract     (#PCDATA)>
<!ELEMENT keyword      (#PCDATA)>
<!ELEMENT last_updated (#PCDATA)>
<!ELEMENT copyright    (#PCDATA)>
<!ELEMENT first_name   (#PCDATA)>
<!ELEMENT middle_name  (#PCDATA)>
<!ELEMENT last_name    (#PCDATA)>
<!ELEMENT title        (#PCDATA)>
<!ELEMENT year         (#PCDATA)>
<!ELEMENT instruments  (#PCDATA)>
<!ELEMENT publisher    (#PCDATA)>
<!ELEMENT length       (#PCDATA)>

Comments in DTDs

• DTDs seem fundamentally more obfuscated than C.

• Comments can improve this by giving example elements

• Comments are the same as in HTML; e.g. <!-- Comment -->

<!-- e.g. "1999 New York Women Composers", 
     not "Copyright 1999 New York Women Composers" -->
<!ELEMENT copyright (#PCDATA)>

Child Elements

    <date><year>1994</year></date> 

• To declare that a date element must have a year child:

<!ELEMENT date (year)>

Child Elements

You only have to declare the immediate children

   <maintainer email="elharo@metalab.unc.edu" 
              url="http://www.elharo.com/">
    <name>
      <first_name>Elliotte</first_name> 
      <middle_name>Rusty</middle_name> 
      <last_name>Harold</last_name>
    </name>
  </maintainer>

  <composer id="c1">
    <name>
      <first_name>Julie</first_name> 
      <middle_name></middle_name> 
      <last_name>Mandel</last_name>
    </name>
  </composer> 

• To declare that a maintainer element must have a name child:

<!ELEMENT maintainer (name)>
<!ELEMENT composer (name)>

Sequences

    <name>
      <first_name>Elliotte</first_name> 
      <middle_name>Rusty</middle_name> 
      <last_name>Harold</last_name>
    </name>

• Separate multiple required child elements with commas; e.g.

  <!ELEMENT name (first_name, middle_name, last_name)>
  

• A list of child elements separated by commas is called a sequence

More Sequences

• The element being described must have only child elements, no mixed content

• You must know the order of the child elements

• You must know the type of each child element

• You must know the number of child elements

• The number can be relaxed with wild cards

One or More Children +

  <cataloging_info>
    <abstract>Compositions by the members of New York Women Composers</abstract>
    <keyword>music publishing</keyword>
    <keyword>scores</keyword>
    <keyword>women composers</keyword>
    <keyword>New York</keyword>
  </cataloging_info>

• The + suffix indicates that one or more of that element is required at that point

<!ELEMENT cataloging_info (abstract, keyword+)>

Zero or More Children *

• The * suffix indicates that zero, one, or more of that element is required at that point

<!ELEMENT catalog (category, cataloging_info, last_updated, copyright, 
                   maintainer, composer*, composition*)>

Zero or One Children ?

  <composition composer="c1">
    <title>Trio for Flute, Viola and Harp</title>
    <date><year>1994</year></date> 
    <length>13'38"</length>
    <instruments>fl, hp, vla</instruments>
    <description>
      <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
      Christine Ims, and Susan Jolles. In 3 movements :</p>
      <ul>
        <li>mvt. 1: 5:01</li>
        <li>mvt. 2: 4:11</li>
        <li>mvt. 3: 4:26</li>
      </ul>  
    </description>
    <publisher>Theodore Presser</publisher>
  </composition>

• Suffixing an element name with a question mark (?) in the content model indicates that either 0 or 1 (but not more than one) of that element are expected at that position

<!ELEMENT composition 
   (title, date, length?, instruments, description?, publisher?)>

Choices

• A choice indicates one element or another but not both

• A choice is signified by a vertical bar |

• There can be two or more elements in a choice

<!ELEMENT date (year | ISODate)>
<!ELEMENT year (#PCDATA)>
<!ELEMENT ISODate (#PCDATA)>

Grouping With Parentheses

• Parentheses combine several elements into a single element.

• Parenthesized elements can be nested inside other parentheses in place of a single element.

• The parenthesized elements can be suffixed with a plus sign, a comma, or a question mark.

<!ELEMENT dl (dt, dd)*>
<!ELEMENT ARTICLE (TITLE, (P | PHOTO | GRAPH | SIDEBAR | PULLQUOTE | SUBHEAD)*, BYLINE?)>

<ELEMENT catalog (category, cataloging_info, last_updated, 
   copyright, maintainer, (composer | composition)*)>

Mixed Content

<!ELEMENT description (#PCDATA | ul | a | cite | p)*>
<!ELEMENT cite (#PCDATA | a)*>
<!ELEMENT ul   (li*)>
<!ELEMENT li   (#PCDATA)>
<!ELEMENT a    (#PCDATA)>
<!ELEMENT p    (#PCDATA)>

• Mixed content is both #PCDATA and child elements in a choice, followed by an asterisk

• This is the only way to combine PCDATA with child elements in a content specification

  • #PCDATA must come first

  • #PCDATA cannot be used in a sequence

Empty elements

<!ELEMENT BR  EMPTY>
<!ELEMENT IMG EMPTY>
<!ELEMENT HR  EMPTY>

Content Specifications DTDs Can't Declare

• Mixed content with other content models

• Exactly one element of a given type but in any position (The SGML & operator)

• Between M and N of a given element

• Restrictions on the PCDATA; e.g. that the year element must contain a four-digit year

Attribute Declarations

Recall this element:

  <maintainer email="elharo@metalab.unc.edu" 
              url="http://www.elharo.com/">
    <name>
      <first_name>Elliotte</first_name> 
      <middle_name>Rusty</middle_name> 
      <last_name>Harold</last_name>
    </name>
  </maintainer>

It is declared like this:

<!ELEMENT maintainer (name)>
<!ATTLIST maintainer email CDATA "webmaster@nywc.org">
<!ATTLIST maintainer url CDATA "http://www.ibiblio.org/nywc">

The general format of an <!ATTLIST> declaration is:

<!ATTLIST Element_name Attribute_name Type Default_value>

Multiple Attribute Declarations

  <maintainer email="elharo@metalab.unc.edu" 
              url="http://www.elharo.com/">
    <name>
      <first_name>Elliotte</first_name> 
      <middle_name>Rusty</middle_name> 
      <last_name>Harold</last_name>
    </name>
  </maintainer>

It is declared like this:

<!ELEMENT maintainer (name)>
<!ATTLIST maintainer email CDATA "webmaster@nywc.org">
<!ATTLIST maintainer url CDATA "http://www.ibiblio.org/nywc">

But it can also be declared in a single <!ATTLIST> declaration like this:

<!ATTLIST maintainer email CDATA "webmaster@nywc.org" url CDATA "http://www.ibiblio.org/nywc/">

This is more obvious with better indentation:

<!ATTLIST maintainer email CDATA "webmaster@nywc.org" 
                     url   CDATA "http://www.ibiblio.org/nywc/">
                     

Attribute Default Values

• A literal string value

• One of these three keywords

• #REQUIRED

• #IMPLIED

• #FIXED

#REQUIRED

• No default value is provided in the DTD

• Document authors must provide an attribute value for each element

<!ELEMENT maintainer (name)>
<!ATTLIST maintainer email CDATA #REQUIRED 
                     url   CDATA #REQUIRED>

#IMPLIED

<!ELEMENT a (#PCDATA)>
<!ATTLIST a href CDATA #IMPLIED>

• No default value in the DTD

• Author may (but does not have to) provide a value with each element

#FIXED

• Value is the same for all elements

• Default value must be provided in DTD

• Document author may not change default value

<!ELEMENT maintainer (name)>
<!ATTLIST maintainer email CDATA #FIXED "webmaster@nywc.org" 
                     url   CDATA #REQUIRED>

Attribute Types

• CDATA

• ID

• IDREF

• IDREFS

• ENTITY

• ENTITIES

• NOTATION

• NMTOKEN

• NMTOKENS

• Enumerated

CDATA

• Most general attribute type

• Value can be any string of text not containing a raw less-than sign (<) or quotation marks (")

<!ATTLIST maintainer email CDATA #REQUIRED 
                     url   CDATA #IMPLIED>

ID

• Value must be an XML name

  • May include letters, digits, underscores, hyphens, and periods

  • May not include whitespace

  • May or may not have the name "id" or "ID"

  • May contain colons only if used for namespaces

• Value must be unique within ID type attributes in the document

• Generally the default value is #REQUIRED

<!ELEMENT composer (name)>
<!ATTLIST composer id ID #REQUIRED>

IDREF

• Value matches the ID of an element in the same document

• Used for links and the like

• Multiple elements may share the same IDREF values

<!ELEMENT composition (title, date, length?, 
   instruments, description?, publisher?)>
<!ATTLIST composition composer IDREF #REQUIRED>

IDREFS

• A list of ID values in the same document

• Separated by white space

<!ELEMENT composition (title, date, length?, 
   instruments, description?, publisher?)>
<!ATTLIST composition composer IDREFS #REQUIRED>

Enumerated

• Not a keyword

• Refers to a list of possible values from which one must be chosen

• Default value is generally provided explicitly

<!ATTLIST P VISIBLE (TRUE | FALSE) "TRUE">

Finished DTD

<!ELEMENT category     (#PCDATA)>
<!ELEMENT abstract     (#PCDATA)>
<!ELEMENT keyword      (#PCDATA)>
<!ELEMENT last_updated (#PCDATA)>
<!ELEMENT copyright    (#PCDATA)>
<!ELEMENT title        (#PCDATA)>
<!ELEMENT instruments  (#PCDATA)>
<!ELEMENT publisher    (#PCDATA)>
<!ELEMENT length       (#PCDATA)>

<!ELEMENT date    (year | ISODate)>
<!ELEMENT year    (#PCDATA)>
<!ELEMENT ISODate (#PCDATA)>

<!ELEMENT catalog (category, cataloging_info, last_updated, 
   copyright, maintainer, (composer | composition)*)>

<!ELEMENT cataloging_info (abstract, keyword+)>

<!ELEMENT description (#PCDATA | ul | a | cite | p)*>
<!ELEMENT cite        (#PCDATA | a)*>
<!ELEMENT ul          (li*)>
<!ELEMENT li          (#PCDATA)>
<!ELEMENT a           (#PCDATA)>
<!ELEMENT p           (#PCDATA)>

<!ELEMENT maintainer  (name)>
<!ELEMENT name        (first_name, middle_name, last_name)>
<!ELEMENT first_name  (#PCDATA)>
<!ELEMENT middle_name (#PCDATA)>
<!ELEMENT last_name   (#PCDATA)>
<!ATTLIST maintainer email CDATA #REQUIRED 
                     url   CDATA #IMPLIED>
                     
<!ELEMENT composer (name)>
<!ATTLIST composer id ID #REQUIRED>

<!ELEMENT composition (title, date, length?, instruments, description?, publisher?)>
<!ATTLIST composition composer IDREFS #REQUIRED>

<!ATTLIST a href CDATA #REQUIRED>

General Entity References

• An abbreviation for commonly used or hard to type text

• Begin with an ampersand and end with a semicolon

  α
  "
  &copyright;
  &signature;
  

• Declared in a <!ENTITY> declaration

  <!ENTITY copyright "Copyright 2000">   
  <!ENTITY quot "&#34;">   
  <!ENTITY signature 
    "<SIGNATURE>
       <COPYRIGHT>2000 Elliotte Rusty Harold</COPYRIGHT>
       <EMAIL>elharo@metalab.unc.edu</EMAIL>
       <LAST_MODIFIED>March 10, 2000</LAST_MODIFIED>
     </SIGNATURE>"
  >   
  

General Entity Reference Example

<?xml version="1.0" standalone="yes"?>
<!DOCTYPE DOCUMENT [

   <!ENTITY ERH "Elliotte Rusty Harold">

   <!ELEMENT DOCUMENT  (TITLE, SIGNATURE)>
   <!ELEMENT TITLE     (#PCDATA)>
   <!ELEMENT COPYRIGHT (#PCDATA)>
   <!ELEMENT EMAIL     (#PCDATA)>
   <!ELEMENT LAST_MODIFIED (#PCDATA)>
   <!ELEMENT SIGNATURE (COPYRIGHT, EMAIL, LAST_MODIFIED)>
]>
<DOCUMENT>
  <TITLE>&ERH;</TITLE>
  <SIGNATURE>
    <COPYRIGHT>1999 &ERH;</COPYRIGHT>
    <EMAIL>elharo@metalab.unc.edu</EMAIL>
    <LAST_MODIFIED>March 10, 1999</LAST_MODIFIED>
   </SIGNATURE>
</DOCUMENT>

External General Entity References

• A general entity reference that refers to a different file

• Parsed and Unparsed

A DTD that declares External General Entities

<!ENTITY AlLeiter         SYSTEM "mets/AlLeiter.xml">
<!ENTITY ArmandoReynoso   SYSTEM "mets/ArmandoReynoso.xml">
<!ENTITY BobbyJones       SYSTEM "mets/BobbyJones.xml">
<!ENTITY BradClontz       SYSTEM "mets/BradClontz.xml">
<!ENTITY DennisCook       SYSTEM "mets/DennisCook.xml">
<!ENTITY GregMcmichael    SYSTEM "mets/GregMcMichael.xml">
<!ENTITY HideoNomo        SYSTEM "mets/HideoNomo.xml">
<!ENTITY JohnFranco       SYSTEM "mets/JohnFranco.xml">
<!ENTITY JosiasManzanillo SYSTEM "mets/JosiasManzanillo.xml">
<!ENTITY OctavioDotel     SYSTEM "mets/OctavioDotel.xml">
<!ENTITY RickReed         SYSTEM "mets/RickReed.xml">
<!ENTITY RigoBeltran      SYSTEM "mets/RigoBeltran.xml">
<!ENTITY WillieBlair      SYSTEM "mets/WillieBlair.xml">

An External Parsed General Entity

• Prolog is only a text declaration

• Document is not valid and may not be well-formed because it may not have a root element.

<?xml version="1.0" encoding="UTF-8"?>
<PLAYER>
  <GIVEN_NAME>Al</GIVEN_NAME>
  <SURNAME>Leiter</SURNAME>
  <P>Starting Pitcher</P>
  <G>28</G>
  <GS>28</GS>
  <W>17</W>
  <L>6</L>
  <SV>0</SV>
  <CG>4</CG>
  <SO>2</SO>
  <ERA>2.47</ERA>
  <IP>193</IP>
  <HRA>8</HRA>
  <RA>55</RA>
  <ER>53</ER>
  <HB>11</HB>
  <WP>4</WP>
  <B>1</B>
  <WB>71</WB>
  <K>174</K>
</PLAYER>

A Document that uses External General Entity References

<?xml version="1.0" standalone="no"?>
<!DOCTYPE TEAM SYSTEM "team.dtd" [
  <!ENTITY % players SYSTEM "mets.dtd"> 
  %players;
  ]
>
<TEAM>
  <TEAM_CITY>New York</TEAM_CITY>
  <TEAM_NAME>Mets</TEAM_NAME>
  &AlLeiter;
  &ArmandoReynoso;
  &BobbyJones;
  &BradClontz;
  &DennisCook;
  &GregMcmichael;
  &HideoNomo;
  &JohnFranco;
  &JosiasManzanillo;
  &OctavioDotel;
  &RickReed;
  &RigoBeltran;
  &WillieBlair;
</TEAM>

Parameter Entity References

• Only used in DTDs

• Use a % instead of an &:

  %inlines;
  %block;
  %mathml-prefix;
  %mathml-colon;
  

• Declared in a <!ENTITY %> declaration

  <!ENTITY % ERH "Elliotte Rusty Harold">   
  <!ENTITY COPY99 "Copyright 1999 %ERH;"> 
  <!ENTITY % inlines 
    "(PERSON | DEGREE | MODEL | PRODUCT | ANIMAL | INGREDIENT)*">
  <!ELEMENT PARAGRAPH %inlines;>
  <!ELEMENT CELL      %inlines;>
  <!ELEMENT HEADING   %inlines;>   
  

External Parameter Entity References

• Only used in DTDs

• Pull in other DTD fragments

• Add a SYSTEM to the declaration:

  <!ENTITY % player SYSTEM "player.dtd">
  %player;
  

• Can use a full URL:

  <!ENTITY % player SYSTEM "http://www.cafeconleche.org/dtds/player.dtd">
  %player;
  

The description element

    <description>
      <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
      Christine Ims, and Susan Jolles. In 3 movements :</p>
      <ul>
        <li>mvt. 1: 5:01</li>
        <li>mvt. 2: 4:11</li>
        <li>mvt. 3: 4:26</li>
      </ul>  
    </description>

<!ELEMENT description (#PCDATA | ul | a | cite | p)*>
<!ELEMENT cite (#PCDATA | a)*>
<!ELEMENT ul (li*)>
<!ELEMENT li (#PCDATA)>
<!ELEMENT p (#PCDATA)>
<!ELEMENT a (#PCDATA)>
<!ATTLIST a href CDATA #IMPLIED>

XHTML

• XHTML is a reformulation of HTML as strict XML

  • Tags must be closed

  • Attribute values must be quoted

  • <br/> instead of <br>

  • etc.

• W3C Recommendation 26 January 2000

• Includes three DTDs for HTML:

  • Strict

  • Transitional

  • Frameset

• What if we can use one of those DTDs instead of inventing our own?

External Parameter Entity References

<!ENTITY % xhtml1 SYSTEM "http://www.w3.org/TR/xhtml1/DTD/strict.dtd">
%xhtml1;

Finished DTD

<!ENTITY % xhtml1 SYSTEM "http://www.w3.org/TR/xhtml1/DTD/strict.dtd">
%xhtml1;

<!ELEMENT category (#PCDATA)>
<!ELEMENT abstract (#PCDATA)>
<!ELEMENT keyword (#PCDATA)>
<!ELEMENT last_updated (#PCDATA)>

<!-- e.g. "1999 New York Women Composers", 
     not "Copyright 1999 New York Women Composers" -->
<!ELEMENT copyright (#PCDATA)>


<!ELEMENT instruments (#PCDATA)>
<!ELEMENT publisher (#PCDATA)>
<!ELEMENT length (#PCDATA)>

<!ELEMENT date (year | ISODate)>
<!ELEMENT year (#PCDATA)>
<!ELEMENT ISODate (#PCDATA)>

<!ELEMENT catalog (category, cataloging_info, last_updated, 
   copyright, maintainer, (composer | composition)*)>

<!ELEMENT cataloging_info (abstract, keyword+)>

<!ELEMENT description %Block;>

<!ELEMENT maintainer (name)>
<!ELEMENT name (first_name, middle_name, last_name)>
<!ELEMENT first_name (#PCDATA)>
<!ELEMENT middle_name (#PCDATA)>
<!ELEMENT last_name (#PCDATA)>
<!ATTLIST maintainer email CDATA #REQUIRED 
                     url   CDATA #IMPLIED>
                     
<!ELEMENT composer (name)>
<!ATTLIST composer id ID #REQUIRED>

<!ELEMENT composition (title, date, length?, instruments, description?, publisher?)>
<!ATTLIST composition composer IDREFS #REQUIRED>

<!ATTLIST a href CDATA #IMPLIED>

Internal DTD Subsets

<?xml version="1.0"?>
<!DOCTYPE document SYSTEM "http://www.w3.org/TR/xhtml1/DTD/transitional.dtd" [
  <!ELEMENT document %BLOCK; >
]>
<document>
<p>Hello There!</p>
</document>

Schemas

• Use XML syntax to describe the allowed content of an XML document rather than DTD syntax

• Allow restrictions to be placed on PCDATA content; e.g. that the contents of an element must be an integer between 1 and 10

• Area of active research and development

Part III: Namespaces

markup isn't about meaning at all; XML just gives you a way to send a bundle of labeled strings of text, with recursion and internationalization, from point A to point B. Namespaces allow the labels to come from multiple vocabularies, and make it cheap for software to find the labeled chunks it cares about.

--Tim Bray on the xml-dev mailing list

Raison d'etre

1. To distinguish between elements and attributes from different vocabularies with different meanings.

2. To group all related elements and attributes together so that a parser can easily recognize them.

The Need for Namespaces

• The XLink specification defines an attribute with the name href. The XHTML specification also uses href attributes on some elements. And the XInclude specification uses href attributes.

• An XSLT style sheet that will transform XHTML documents containing both Scalable Vector Graphics (SVG) pictures and MathML equations into XSL-Formatting object documents.

  • The a, title, script, style and font elements in XHTML and SVG

  • The table element in XHTML and XSL-FO

  • The text element in XSLT and SVG

  • The set element in MathML and SVG

• An XSLT stylesheet that transforms a style sheet in an older version of the XSLT specification to a style sheet in a newer version of the XSLT specification.

Namespaces disambiguate elements

• Namespaces disambiguate elements with the same name from each other by attaching different prefixes to names from different XML applications.

• Each prefix is associated with a URI.

  • Names whose prefixes are associated with the same URI are in the same namespace.

  • Names whose prefixes are associated with different URIs are in different namespaces.

Namespace Syntax

• Elements and attributes that are in namespaces have names that contain exactly one colon. They look like this:

  rdf:description
  xlink:type
  xsl:template
  

• Everything before the colon is called the prefix

• Everything after the colon is called the local part.

• The complete name including the colon is called the qualified name.

Namespace URIs

• Each prefix in a qualified name is associated with a URI.

• For example, all elements in XSLT 1.0 style sheets are associated with the http://www.w3.org/1999/XSL/Transform URI.

• The customary prefix xsl is a shorthand for the longer URI http://www.w3.org/1999/XSL/Transform.

• You can't use the URI in the element name directly.

  {http://www.w3.org/1999/XSL/Transform}template

Binding Prefixes to Namespace URIs

• Prefixes are bound to namespace URIs by attaching an xmlns:prefix attribute to the prefixed element or one of its ancestors.

  <svg:svg xmlns:svg="http://www.w3.org/2000/svg" 
   width="12cm" height="10cm">
    <svg:ellipse rx="110" ry="130" />
    <svg:rect x="4cm" y="1cm" width="3cm" height="6cm" />
  </svg:svg>
  

• Bindings have scope within the element where they're declared.

• An SVG processor can recognize all three of these elements as SVG elements because they all have prefixes bound to the particular URI defined by the SVG specification.

Binding Prefixes to Namespace URIs Example

<xhtml:html xmlns:xhtml="http://www.w3.org/1999/xhtml"
            xmlns:xlink="http://www.w3.org/1999/xlink">
  <xhtml:head><xhtml:title>Three Namespaces</xhtml:title></xhtml:head>
  <xhtml:body>
    <xhtml:h1 align="center">An Ellipse and a Rectangle</xhtml:h1>
    <svg:svg xmlns:svg="http://www.w3.org/2000/svg" 
             width="12cm" height="10cm">
      <svg:ellipse rx="110" ry="130" />
      <svg:rect x="4cm" y="1cm" width="3cm" height="6cm" />
    </svg:svg>
    <xhtml:p xlink:type="simple" 
      xlink:href="ellipses.html">
      More about ellipses
    </xhtml:p>
    <xhtml:p xlink:type="simple" xlink:href="rectangles.html">
      More about rectangles
    </xhtml:p>
    <xhtml:hr/>
    <xhtml:p>Last Modified February 13, 2000</xhtml:p>    
  </xhtml:body>
</xhtml:html>

Binding namespaces to prefixes with #FIXED ATTLIST declarations

<!ATTLIST svg:svg xmlns:svg (CDATA) #FIXED "http://www.w3.org/2000/svg">

<svg:svg width="12cm" height="10cm">
  <svg:ellipse rx="110" ry="130" />
  <svg:rect x="4cm" y="1cm" width="3cm" height="6cm" />
</svg:svg>

Unprefixed attributes are never in any namespace

• Unprefixed attributes are never in any namespace.

• Being an attribute of an element in the http://www.w3.org/1999/xhtml namespace is not sufficient to put the attribute in the http://www.w3.org/1999/xhtml namespace.

• The only way an attribute belongs to a namespace is if it has a declared prefix, like xlink:type and xlink:href.

URIs matter; not prefixes

• Many XML applications have recommended prefixes. For example, SVG elements often use the prefix svg and Resource Description Framework (RDF) elements often have the prefix rdf. However, these prefixes are simply conventions, and can be changed based on necessity, convenience or whim.

• Before a prefix can be used, it must be bound to a URI.

• These URIs are standardized, not the prefixes.

• The prefix can change as long as the URI stays the same.

Namespace URIs do not necessarily point to a document, page, or schema

• Purely formal

• Can point somewhere but do not have to

• Parsers compare namespace URIs on a character by character basis. These are three different namespaces:

  • http://www.w3.org/1999/XSL/Transform

  • http://www.w3.org/1999/XSL/Transform/

  • http://www.w3.org/1999/XSL/Transform/index.html

The Default Namespace

• Indicate that an unprefixed element and all its unprefixed descendant elements belong to a particular namespace by attaching an xmlns attribute with no prefix:

  <DATASCHEMA xmlns="http://www.w3.org/2000/P3Pv1">
    <DATA name="vehicle.make" type="text" short="Make" 
          category="preference" size="31"/>
    <DATA name="vehicle.model" type="text" short="Model" 
          category="preference" size="31"/>
    <DATA name="vehicle.year" type="number" short="Year" 
          category="preference" size="4"/>
    <DATA name="vehicle.license.state." type="postal." short="State" 
          category="preference" size="2"/>
    <DATA name="vehicle.license.number" type="text" 
          short="License Plate Number" category="preference" size="12"/>
  </DATASCHEMA>
  

• Both the DATASCHEMA and DATA elements are in the http://www.w3.org/2000/P3Pv1 namespace.

• Default namespaces apply only to elements, not to attributes. Thus in the above example the name, type, short, category, and size attributes are not in any namespace.

• You can change the default namespace within a particular element by adding an xmlns attribute to the element.

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:xlink="http://www.w3.org/XML/XLink/0.9">
  <head><title>Three Namespaces</title></head>
  <body>
    <h1 align="center">An Ellipse and a Rectangle</h1>
    <svg xmlns="http://www.w3.org/2000/svg" 
         width="12cm" height="10cm">
      <ellipse rx="110" ry="130" />
      <rect x="4cm" y="1cm" width="3cm" height="6cm" />
    </svg>
    <p xlink:type="simple" xlink:href="ellipses.html">
      More about ellipses
    </p>
    <p xlink:type="simple" xlink:href="rectangles.html">
      More about rectangles
    </p>
    <hr/>
    <p>Last Modified February 13, 2000</p>    
  </body>
</html>

Binding default namespaces to elements with #FIXED ATTLISTs

<!ATTLIST svg xmlns (CDATA) #FIXED "http://www.w3.org/2000/svg">

<svg width="12cm" height="10cm">
  <ellipse rx="110" ry="130" />
  <rect x="4cm" y="1cm" width="3cm" height="6cm" />
</svg>

How Parsers Handle Namespaces

• Namespaces were added to XML 1.0 after the fact, but care was taken to ensure backwards compatibility.

• An XML 1.0 parser that does not know about namespaces will most likely not have any troubles reading a document that uses namespaces.

• A namespace aware parser also checks to see that all prefixes are mapped to URIs. Otherwise it behaves almost exactly like a non-namespace aware parser.

• Other software that sits on top of the raw XML parser, an XSLT engine for example, may treat elements differently depending on what namespace they belong to. However, the XML parser itself mostly doesn't care as long as all well- formedness and namespace constraints are met.

• A possible exception occurs in the unlikely event that elements with different prefixes belong to the same namespace or elements with the same prefix belong to different namespaces

• Many parsers have the option of whether to report namespace violations so that you can turn namespace processing on or off as you see fit.

Namespaces and DTDs

• DTDs must declare the qualified names

  <!ELEMENT svg:text (#PCDATA)>

• If the prefix changes, the DTD needs to change to.

• Parameter entity references can help when the prefix changes or is removed:

  <!ENTITY % mathml-colon      ''>
  <!ENTITY % mathml-prefix     ''>
  
  <!ENTITY % mathml-exp        '%mathml-prefix;%mathml-colon;exp' >
  <!ENTITY % mathml-abs        '%mathml-prefix;%mathml-colon;abs' >
  <!ENTITY % mathml-arg        '%mathml-prefix;%mathml-colon;arg' >
  <!ENTITY % mathml-real       '%mathml-prefix;%mathml-colon;real' >
  <!ENTITY % mathml-imaginary  '%mathml-prefix;%mathml-colon;imaginary' >
  
  <!ELEMENT %mathml-prefix;%mathml-colon;%mathml-exp; EMPTY>
  

Part IV: XSL, the Extensible Stylesheet Language

people are won over to XSLT once they have a chance to get some perspective, and this usually doesn't take long at all. I have had much occasion working with developers who curse and splutter all the time at all the little tripping points of XSLT that Mike Kay points out. But at least twice, I remember a developer saying, after a few days of this, something to the effect of "wow, XSLT is certainly a different way of thinking, but I must say that I accomplished my XML processing task using XSLT in a fraction of the time it took for me to do the same with DOM and Java".

--Uche Ogbuji on the xml-dev mailing list, Mon, 25 Mar 2002

What Is XSL?

• The Extensible Stylesheet Language

• Two parts:

  • A transformation language (XSLT)

  • A formatting language (XSL-FO)

Versions

• This talk covers:

  • XSL Transformations: November 16, 1999 1.0 Specification

  • XPath: November 16, 1999 1.0 Specification

• XSLT 2.0 is under development.

The Process of an XSL Transformation

1. The XML parser reads an XML document and forms a tree

2. The tree is passed to the XSLT processor

3. The XSLT processor compares the nodes in the tree to the instructions in the style sheet

4. When the XSLT processor finds a match, it outputs a tree fragment

5. (Optional) The complete output tree is serialized to some other format such as text, HTML, or an XML file

An Example XML Document

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE catalog SYSTEM "compositions.dtd">
<catalog>

  <category>
    Small chamber ensembles - 2-4 Players by New York Women Composers
  </category>

  <cataloging_info>
    <abstract>Compositions by the members of New York Women Composers</abstract>
    <keyword>music publishing</keyword>
    <keyword>scores</keyword>
    <keyword>women composers</keyword>
    <keyword>New York</keyword>
  </cataloging_info>

  <last_updated>July 28, 1999</last_updated>
  <copyright>1999 New York Women Composers</copyright>
  <maintainer email="elharo@metalab.unc.edu" 
              url="http://www.elharo.com/">
    <name>
      <first_name>Elliotte</first_name> 
      <middle_name>Rusty</middle_name> 
      <last_name>Harold</last_name>
    </name>
  </maintainer>

  <composer id="c1">
    <name>
      <first_name>Julie</first_name> 
      <middle_name></middle_name> 
      <last_name>Mandel</last_name>
    </name>
  </composer>

  <composer id="c2">
    <name>
      <first_name>Margaret</first_name> 
      <middle_name>De</middle_name> 
      <last_name>Wys</last_name>
    </name>
  </composer>  
    
  <composer id="c3">
    <name>
      <first_name>Beth</first_name> 
      <middle_name></middle_name> 
      <last_name>Anderson</last_name>
    </name>
  </composer>
    
  <composer id="c4">
    <name>
      <first_name>Linda</first_name> 
      <middle_name></middle_name> 
      <last_name>Bouchard</last_name>
    </name>
  </composer>
    
  <composition composer="c1">
    <title>Trio for Flute, Viola and Harp</title>
    <date><year>1994</year></date> 
    <length>13'38"</length>
    <instruments>fl, hp, vla</instruments>
    <description>
      <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
      Christine Ims, and Susan Jolles. In 3 movements :</p>
      <ul>
        <li>mvt. 1: 5:01</li>
        <li>mvt. 2: 4:11</li>
        <li>mvt. 3: 4:26</li>
      </ul>  
    </description>
    <publisher>Theodore Presser</publisher>
  </composition>

  <composition composer="c2">
    <title>Charmonium</title>
    <date><year>1991</year></date> 
    <length>9'</length>
    <instruments>2 vln, vla, vc</instruments>
    <description>
      <p>Commissioned as quartet for the Meridian String Quartet. 
      Sonorous, bold. Moderate difficulty. Tape available.</p>
    </description> 
  </composition>

  <composition composer="c1">
    <title>Invention for Flute and Piano</title>
    <date><year>1994</year></date> 
    <instruments>fl, pn</instruments>
    <description><p>3 movements</p></description> 
  </composition>

  <composition composer="c3">
    <title>Little Trio</title>
    <date><year>1984</year></date> 
    <length>4'</length>
    <instruments>fl, guit, va</instruments>
    <publisher>ACA</publisher>
  </composition>

  <composition composer="c3">
    <title>Dr. Blood's Mermaid Lullaby</title>
    <date><year>1980</year></date> 
    <length>3'</length>
    <instruments>fl or ob, or vn, or vc, pn</instruments>
    <publisher>ACA</publisher>
  </composition>

  <composition composer="c3">
    <title>Trio: Dream in D</title>
    <date><year>1980</year></date> 
    <length>10'</length>
    <instruments>fl, pn, vc, or vn, pn, vc</instruments>
    <description>
      <p>Rhapsodic. Passionate. Available on CD 
      <cite>
      <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/">
      Two by Three</a></cite> 
      from North/South Consonance (1998).</p>
    </description> 
  </composition>

  <composition composer="c4">
    <title>Propos II</title>
    <date><year>1985</year></date> 
    <length>11'</length>
    <instruments>2 tpt</instruments>
    <description><p>Arrangement from Propos</p></description> 
  </composition>

  <composition composer="c4">
    <title>Rictus En Mirroir</title>
    <date><year>1985</year></date> 
    <length>14'</length>
    <instruments>fl, ob, hpschd, vc</instruments>
  </composition>

</catalog>

An XSLT Style Sheet

<?xml version="1.0"?>
<xsl:stylesheet version="1.0" 
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

</xsl:stylesheet>

Using SAXON to apply the stylesheet to compositions.xml

• Windows executable:

  C:\>saxon compositions.xml sheet1.xsl
  

• Java executable:

  C:\>java com.icl.saxon.StyleSheet compositions.xml sheet1.xsl output1.html
  <html>
  ...
  

Output

<?xml version="1.0" encoding="utf-8"?>

  
    Small chamber ensembles - 2-4 Players by New York Women Composers
  

  
    Compositions by the members of New York Women Composers
    music publishing
    scores
    women composers
    New York
  

  July 28, 1999
  1999 New York Women Composers
  
    
      Elliotte 
      Rusty 
      Harold
    
  

  
    
      Julie 
       
      Mandel
    
  

  
    
      Margaret 
      De 
      Wys
    
    
    
  
    
      Beth 
       
      Anderson
    
  
    
  
    
      Linda 
       
      Bouchard
    
  
    
  
    Trio for Flute, Viola and Harp
    1994 
    13'38"
    fl, hp, vla
    
      Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
      Christine Ims, and Susan Jolles. In 3 movements :
      
        mvt. 1: 5:01
        mvt. 2: 4:11
        mvt. 3: 4:26
        
    
    Theodore Presser
  

  
    Charmonium
    1991 
    9'
    2 vln, vla, vc
    
      Commissioned as quartet for the Meridian String Quartet. 
      Sonorous, bold. Moderate difficulty. Tape available.
     
  

  
    Invention for Flute and Piano
    1994 
    fl, pn
    3 movements 
  

  
    Little Trio
    1984 
    4'
    fl, guit, va
    ACA
  

  
    Dr. Blood's Mermaid Lullaby
    1980 
    3'
    fl or ob, or vn, or vc, pn
    ACA
  

  
    Trio: Dream in D
    1980 
    10'
    fl, pn, vc, or vn, pn, vc
    
      Rhapsodic. Passionate. Available on CD 
      
      
      Two by Three 
      from North/South Consonance (1998).
     
  

  
    Propos II
    1985 
    11'
    2 tpt
    Arrangement from Propos 
  

  
    Rictus En Mirroir
    1985 
    14'
    fl, ob, hpschd, vc
  

Templates

<?xml version="1.0"?>
<xsl:stylesheet version="1.0" 
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template match="composition">
    <h3><xsl:value-of select="title"/></h3>
  </xsl:template>

</xsl:stylesheet>

The actual HTML output

<?xml version="1.0" encoding="utf-8"?>

  
    Small chamber ensembles - 2-4 Players by New York Women Composers
  

  
    Compositions by the members of New York Women Composers
    music publishing
    scores
    women composers
    New York
  

  July 28, 1999
  1999 New York Women Composers
  
    
      Elliotte 
      Rusty 
      Harold
    
  

  
    
      Julie 
       
      Mandel
    
  

  
    
      Margaret 
      De 
      Wys
    
    
    
  
    
      Beth 
       
      Anderson
    
  
    
  
    
      Linda 
       
      Bouchard
    
  
    
  <h3>Trio for Flute, Viola and Harp</h3>

  <h3>Charmonium</h3>

  <h3>Invention for Flute and Piano</h3>

  <h3>Little Trio</h3>

  <h3>Dr. Blood's Mermaid Lullaby</h3>

  <h3>Trio: Dream in D</h3>

  <h3>Propos II</h3>

  <h3>Rictus En Mirroir</h3>

Adding the root

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" 
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template match="/">
    <html>
      <body>        
        
      </body>
    </html>
  </xsl:template>

  <xsl:template match="composition">
    <h3><xsl:value-of select="title"/></h3>
  </xsl:template>

</xsl:stylesheet>

The actual HTML output

<html>
   <body></body>
</html>

Applying Templates

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" 
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template match="/">
    <html>
      <body>
        <xsl:apply-templates/>
      </body>
    </html>
  </xsl:template>

  <xsl:template match="composition">
    <h3><xsl:value-of select="title"/></h3>
  </xsl:template>

</xsl:stylesheet>

The actual HTML output

<html>
   <body>
      
      
      Small chamber ensembles - 2-4 Players by New York Women Composers
      
      
      
      Compositions by the members of New York Women Composers
      music publishing
      scores
      women composers
      New York
      
      
      July 28, 1999
      1999 New York Women Composers
      
      
      Elliotte 
      Rusty 
      Harold
      
      
      
      
      
      Julie 
       
      Mandel
      
      
      
      
      
      Margaret 
      De 
      Wys
      
        
      
      
      
      Beth 
       
      Anderson
      
      
      
      
      
      Linda 
       
      Bouchard
      
      
      
      
      <h3>Trio for Flute, Viola and Harp</h3>
      
      
      <h3>Charmonium</h3>
      
      
      <h3>Invention for Flute and Piano</h3>
      
      
      <h3>Little Trio</h3>
      
      
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      
      
      <h3>Trio: Dream in D</h3>
      
      
      <h3>Propos II</h3>
      
      
      <h3>Rictus En Mirroir</h3>
      
      
   </body>
</html>

The select attribute

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" 
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template match="/">
    <html>
       <xsl:apply-templates select="catalog"/>
    </html>
  </xsl:template>

  <xsl:template match="catalog">
    <head>
       <title><xsl:value-of select="category"/></title>      
    </head>
    <body>
       <h1><xsl:value-of select="category"/></h1>      
       <xsl:apply-templates select="composition"/>
    </body>
  </xsl:template>

  <xsl:template match="composition">
    <h3><xsl:value-of select="title"/></h3>
  </xsl:template>

</xsl:stylesheet>

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h3>Trio for Flute, Viola and Harp</h3>
      <h3>Charmonium</h3>
      <h3>Invention for Flute and Piano</h3>
      <h3>Little Trio</h3>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <h3>Trio: Dream in D</h3>
      <h3>Propos II</h3>
      <h3>Rictus En Mirroir</h3>
   </body>
</html>

Expanding the coverage

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" 
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template match="/">
    <html>
       <xsl:apply-templates select="catalog"/>
    </html>
  </xsl:template>

  <xsl:template match="catalog">
    <head>
       <title><xsl:value-of select="category"/></title>      
    </head>
    <body>
       <h1><xsl:value-of select="category"/></h1>      
       <xsl:apply-templates select="composition"/>
       <hr/>
       Copyright <xsl:value-of select="copyright"/><br/>
       Last Modified: <xsl:value-of select="last_updated"/>
    </body>
  </xsl:template>

  <xsl:template match="composition">
    <h3><xsl:value-of select="title"/></h3>

    <ul>
     <li><xsl:value-of select="date"/></li>
     <li><xsl:value-of select="length"/></li>
     <li><xsl:value-of select="instruments"/></li>
     <li><xsl:value-of select="publisher"/></li>    
    </ul>

    <p><xsl:value-of select="description"/></p>    
    
  </xsl:template>

</xsl:stylesheet>

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
         Christine Ims, and Susan Jolles. In 3 movements :
         
         mvt. 1: 5:01
         mvt. 2: 4:11
         mvt. 3: 4:26
         
         
      </p>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
         <li></li>
      </ul>
      <p>
         Commissioned as quartet for the Meridian String Quartet. 
         Sonorous, bold. Moderate difficulty. Tape available.
         
      </p>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li></li>
         <li>fl, pn</li>
         <li></li>
      </ul>
      <p>3 movements</p>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
         <li></li>
      </ul>
      <p>
         Rhapsodic. Passionate. Available on CD 
         
         
         Two by Three 
         from North/South Consonance (1998).
         
      </p>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
         <li></li>
      </ul>
      <p>Arrangement from Propos</p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
         <li></li>
      </ul>
      <p></p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999
   </body>
</html>

Attributes

• I want to add something like this to the footer so readers can contact me if there's a problem with the page:

  Elliotte Rusty Harold<br/>
  elharo@metalab.unc.edu
  

• This information comes from the maintainer element:

    <maintainer email="elharo@metalab.unc.edu" 
                url="http://www.elharo.com/">
      <name>
        <first_name>Elliotte</first_name> 
        <middle_name>Rusty</middle_name> 
        <last_name>Harold</last_name>
      </name>
    </maintainer>
  

• We need a way to get content from attributes in the input document. This is accomplished by prefixing the attribute name with @.

    <xsl:template match="catalog">
      <head>
         <title><xsl:value-of select="category"/></title>      
      </head>
      <body>
         <h1><xsl:value-of select="category"/></h1>      
         <xsl:apply-templates select="composition"/>
         <hr/>
         Copyright <xsl:value-of select="copyright"/><br/>
         Last Modified: <xsl:value-of select="last_updated"/><br/>
         <xsl:apply-templates select="maintainer"/>
      </body>
    </xsl:template>
  
    <xsl:template match="maintainer">
      <xsl:value-of select="name"/><br/>
      <xsl:value-of select="@email"/>
    </xsl:template>  
  

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
         Christine Ims, and Susan Jolles. In 3 movements :
         
         mvt. 1: 5:01
         mvt. 2: 4:11
         mvt. 3: 4:26
         
         
      </p>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
         <li></li>
      </ul>
      <p>
         Commissioned as quartet for the Meridian String Quartet. 
         Sonorous, bold. Moderate difficulty. Tape available.
         
      </p>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li></li>
         <li>fl, pn</li>
         <li></li>
      </ul>
      <p>3 movements</p>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
         <li></li>
      </ul>
      <p>
         Rhapsodic. Passionate. Available on CD 
         
         
         Two by Three 
         from North/South Consonance (1998).
         
      </p>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
         <li></li>
      </ul>
      <p>Arrangement from Propos</p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
         <li></li>
      </ul>
      <p></p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br>
      Elliotte 
      Rusty 
      Harold
      <br>elharo@metalab.unc.edu
   </body>
</html>

Attribute Value Templates

• Add this to the footer:

    <a href="http://www.elharo.com/">Elliotte Rusty Harold</a><br/>
    <a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a>
  

• Need a way to copy nodes from the input document to attribute values in the output document.

• Attribute value templates are the solution

    <xsl:template match="maintainer">
      <a href="{@url}"><xsl:value-of select="name"/></a><br/>
      <a href="mailto:{@email}"><xsl:value-of select="@email"/></a>
    </xsl:template>
  

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
         Christine Ims, and Susan Jolles. In 3 movements :
         
         mvt. 1: 5:01
         mvt. 2: 4:11
         mvt. 3: 4:26
         
         
      </p>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
         <li></li>
      </ul>
      <p>
         Commissioned as quartet for the Meridian String Quartet. 
         Sonorous, bold. Moderate difficulty. Tape available.
         
      </p>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li></li>
         <li>fl, pn</li>
         <li></li>
      </ul>
      <p>3 movements</p>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
         <li></li>
      </ul>
      <p>
         Rhapsodic. Passionate. Available on CD 
         
         
         Two by Three 
         from North/South Consonance (1998).
         
      </p>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
         <li></li>
      </ul>
      <p>Arrangement from Propos</p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
         <li></li>
      </ul>
      <p></p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.elharo.com/">
         Elliotte 
         Rusty 
         Harold
         
      </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

xsl:copy

• The descriptions in the output document are pure text.

• The descriptions in the input document are somewhat more styled and include paragraphs, unordered lists and citations; e.g.

      <description>
        <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
        Christine Ims, and Susan Jolles. In 3 movements :</p>
        <ul>
          <li>mvt. 1: 5:01</li>
          <li>mvt. 2: 4:11</li>
          <li>mvt. 3: 4:26</li>
        </ul>  
      </description>
  

• But all this is stripped by the default template rule used for the description!

• Use xsl:copy to move these elements into the output more or less as is:

    <xsl:template match="p">
      <xsl:copy>
        <xsl:apply-templates/>
      </xsl:copy>
    </xsl:template>  
    
    <!-- pass HTML along unchanged -->
    <xsl:template match="ul">
      <xsl:copy>
        <xsl:apply-templates"/>
      </xsl:copy>
    </xsl:template>  
    
    <xsl:template match="li">
      <xsl:copy>
        <xsl:apply-templates"/>
      </xsl:copy>
    </xsl:template>  
    
    <xsl:template match="cite">
      <xsl:copy>
        <xsl:apply-templates"/>
      </xsl:copy>
    </xsl:template>  
  

• We also have to apply templates to the description element rather than taking its value:

    <xsl:template match="composition">
      <h3><xsl:value-of select="title"/></h3>
  
      <ul>
       <li><xsl:value-of select="date"/></li>
       <li><xsl:value-of select="length"/></li>
       <li><xsl:value-of select="instruments"/></li>
       <li><xsl:value-of select="publisher"/></li>    
      </ul>
  
      <p><xsl:apply-templates select="description"/></p>    
      
    </xsl:template>
  

The generated HTML

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         
         <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
            Christine Ims, and Susan Jolles. In 3 movements :
         </p>
         
         <ul>
            
            <li>mvt. 1: 5:01</li>
            
            <li>mvt. 2: 4:11</li>
            
            <li>mvt. 3: 4:26</li>
            
         </ul>  
         
      </p>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
         <li></li>
      </ul>
      <p>
         
         <p>Commissioned as quartet for the Meridian String Quartet. 
            Sonorous, bold. Moderate difficulty. Tape available.
         </p>
         
      </p>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li></li>
         <li>fl, pn</li>
         <li></li>
      </ul>
      <p>
         <p>3 movements</p>
      </p>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
         <li></li>
      </ul>
      <p>
         
         <p>Rhapsodic. Passionate. Available on CD 
            <cite>
               
               Two by Three
            </cite> 
            from North/South Consonance (1998).
         </p>
         
      </p>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
         <li></li>
      </ul>
      <p>
         <p>Arrangement from Propos</p>
      </p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
         <li></li>
      </ul>
      <p></p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.macfaq.com/personal.html">
         Elliotte 
         Rusty 
         Harold
         
      </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

The Or Operator in Match Patterns

Since all four template rules for the HTML element have the same content, we can combine them into a single rule that applies to each of the four using the or operator |

  <xsl:template match="p|ul|li|cite">
    <xsl:copy>
      <xsl:apply-templates/>
    </xsl:copy>
  </xsl:template>  

The * wildcard

Right now the descriptions in the input document only use a few HTML tags, but potentially they could use full HTML up to and including tables, images, styles, and more. You could include separate template rules for each of these, but it's easier to specify a rule that applies to all elements.

  <!-- pass unrecognized tags along unchanged -->
  <xsl:template match="*">
    <xsl:copy>
      <xsl:apply-templates/>
    </xsl:copy>
  </xsl:template>  

The * matches all elements that are not matched by some more specific rules. It only matches element nodes, though. It does not match nodes for

• attributes

• comments

• processing instructions

• namespaces

• text

The output is the same in this case, though for a document that used more HTML it might be different.

The node() and @* wildcards

To copy everything including:

• attributes

• comments

• processing instructions

• namespaces

• text

we have to use greedier wild cards:

• @* to copy attribute nodes

• node() to copy all other nodes

  <!-- pass unrecognized nodes along unchanged -->
  <xsl:template match="node()|@*">
    <xsl:copy>
      <xsl:apply-templates select="node()|@*"/>
    </xsl:copy>
  </xsl:template>  

The output is the same in this case, though for a document that used more HTML it might be different.

Are we being too greedy?

Perhaps this is too greedy. Do we really only want to recognize HTML in the description element? What if somebody puts HTML in a different, element like instruments? What if somebody makes a mistake and adds an element that shouldn't be there?

I don't think so, but it would be possible to use modes or other techniques to make this default rule only apply inside the description element.

Testing conditions with xsl:if

  <xsl:template match="composition">
    <h3><xsl:value-of select="title"/></h3>

    <ul>
     <xsl:if test="date">
       <li><xsl:value-of select="date"/></li>
     </xsl:if>
     <xsl:if test="length">
       <li><xsl:value-of select="length"/></li>
     </xsl:if>
     <xsl:if test="instruments">
       <li><xsl:value-of select="instruments"/></li>
     </xsl:if>
     <xsl:if test="publisher">
       <li><xsl:value-of select="publisher"/></li>
     </xsl:if>    
    </ul>

    <p><xsl:apply-templates select="description"/></p>    
    
  </xsl:template>

• Non-empty node-sets are true. Empty node-sets are false.

• Zero length strings are false. Other strings are true.

• There are all the <, >, =, !=, <= and >= operators you expect

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         <description>
            
            <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
               Christine Ims, and Susan Jolles. In 3 movements :
            </p>
            
            <ul>
               
               <li>mvt. 1: 5:01</li>
               
               <li>mvt. 2: 4:11</li>
               
               <li>mvt. 3: 4:26</li>
               
            </ul>  
            
         </description>
      </p>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Commissioned as quartet for the Meridian String Quartet. 
               Sonorous, bold. Moderate difficulty. Tape available.
            </p>
            
         </description>
      </p>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li>fl, pn</li>
      </ul>
      <p>
         <description>
            <p>3 movements</p>
         </description>
      </p>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Rhapsodic. Passionate. Available on CD 
               <cite>
                  <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/" shape="rect">
                     Two by Three
                  </a>
               </cite> 
               from North/South Consonance (1998).
            </p>
            
         </description>
      </p>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
      </ul>
      <p>
         <description>
            <p>Arrangement from Propos</p>
         </description>
      </p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
      </ul>
      <p></p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.elharo.com/">
         Elliotte 
         Rusty 
         Harold
         
      </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

Matching composers with compositions

The composers and their compositions are linked through the the id attribute of the composer element and the composer attribute of the composition element.

  <composer id="c3">
    <name>
      <first_name>Beth</first_name> 
      <middle_name></middle_name> 
      <last_name>Anderson</last_name>
    </name>
  </composer>
    
  <composition composer="c3">
    <title>Trio: Dream in D</title>
    <date><year>(1980)</year></date> 
    <length>10'</length>
    <instruments>fl, pn, vc, or vn, pn, vc</instruments>
    <description>
      Rhapsodic. Passionate. Available on CD 
      <cite><a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid%3D913265342/sr%3D1-2/">Two by Three</a></cite> 
      from North/South Consonance (1998).
    </description> 
    <publisher></publisher>
  </composition>

Matching composers with compositions

  <xsl:template match="catalog">
    <head>
       <title><xsl:value-of select="category"/></title>      
    </head>
    <body>
       <h1><xsl:value-of select="category"/></h1>      
       <xsl:apply-templates select="composer"/>
       <hr/>
       Copyright <xsl:value-of select="copyright"/><br/>
       Last Modified: <xsl:value-of select="last_updated"/><br/>
       <xsl:apply-templates select="maintainer"/>
    </body>
  </xsl:template>
  
  <xsl:template match="composer">
    <h2><xsl:value-of select="name"/></h2>
    <xsl:apply-templates select="../composition[@composer=current()/@id]"/>
  </xsl:template>

• .. selects the parent element

• / selects a child of the context node

• Square braces [] include a predicate to winnow down the selected nodes

• The current() function refers to the matched composer element

• @composer() and @id take the value of the composer attribute and the id attribute

• The = operator compares the to attributes

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h2>
         Julie 
         
         Mandel
         
      </h2>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         <description>
            
            <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
               Christine Ims, and Susan Jolles. In 3 movements :
            </p>
            
            <ul>
               
               <li>mvt. 1: 5:01</li>
               
               <li>mvt. 2: 4:11</li>
               
               <li>mvt. 3: 4:26</li>
               
            </ul>  
            
         </description>
      </p>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li>fl, pn</li>
      </ul>
      <p>
         <description>
            <p>3 movements</p>
         </description>
      </p>
      <h2>
         Margaret 
         De 
         Wys
         
      </h2>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Commissioned as quartet for the Meridian String Quartet. 
               Sonorous, bold. Moderate difficulty. Tape available.
            </p>
            
         </description>
      </p>
      <h2>
         Beth 
         
         Anderson
         
      </h2>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Rhapsodic. Passionate. Available on CD 
               <cite>
                  <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/" shape="rect">
                     Two by Three
                  </a>
               </cite> 
               from North/South Consonance (1998).
            </p>
            
         </description>
      </p>
      <h2>
         Linda 
         
         Bouchard
         
      </h2>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
      </ul>
      <p>
         <description>
            <p>Arrangement from Propos</p>
         </description>
      </p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
      </ul>
      <p></p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.macfaq.com/personal.html">
         Elliotte 
         Rusty 
         Harold
         
      </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

Sorting with xsl:sort

  <xsl:template match="catalog">
    <head>
       <title><xsl:value-of select="category"/></title>      
    </head>
    <body>
       <h1><xsl:value-of select="category"/></h1>      
       <xsl:apply-templates select="composer">
         <xsl:sort select="name/last_name"/>
       </xsl:apply-templates>
       <hr/>
       Copyright <xsl:value-of select="copyright"/><br/>
       Last Modified: <xsl:value-of select="last_updated"/><br/>
       <xsl:apply-templates select="maintainer"/>
    </body>
  </xsl:template>

• The select attribute provides the key to sort by

• Must be a child of xsl:apply-templates or xsl:for-each

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h2>
         Beth 
         
         Anderson
         
      </h2>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Rhapsodic. Passionate. Available on CD 
               <cite>
                  <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/" shape="rect">
                     Two by Three
                  </a>
               </cite> 
               from North/South Consonance (1998).
            </p>
            
         </description>
      </p>
      <h2>
         Linda 
         
         Bouchard
         
      </h2>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
      </ul>
      <p>
         <description>
            <p>Arrangement from Propos</p>
         </description>
      </p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
      </ul>
      <p></p>
      <h2>
         Julie 
         
         Mandel
         
      </h2>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         <description>
            
            <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
               Christine Ims, and Susan Jolles. In 3 movements :
            </p>
            
            <ul>
               
               <li>mvt. 1: 5:01</li>
               
               <li>mvt. 2: 4:11</li>
               
               <li>mvt. 3: 4:26</li>
               
            </ul>  
            
         </description>
      </p>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li>fl, pn</li>
      </ul>
      <p>
         <description>
            <p>3 movements</p>
         </description>
      </p>
      <h2>
         Margaret 
         De 
         Wys
         
      </h2>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Commissioned as quartet for the Meridian String Quartet. 
               Sonorous, bold. Moderate difficulty. Tape available.
            </p>
            
         </description>
      </p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.macfaq.com/personal.html">
         Elliotte 
         Rusty 
         Harold
         
      </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

Multiple Key Sorts

  <xsl:template match="catalog">
    <head>
       <title><xsl:value-of select="category"/></title>      
    </head>
    <body>
       <h1><xsl:value-of select="category"/></h1>      
       <xsl:apply-templates select="composer">
         <xsl:sort select="name/last_name"/>
         <xsl:sort select="name/first_name"/>
         <xsl:sort select="name/middle_name"/>
       </xsl:apply-templates>
       <hr/>
       Copyright <xsl:value-of select="copyright"/><br/>
       Last Modified: <xsl:value-of select="last_updated"/><br/>
       <xsl:apply-templates select="maintainer"/>
    </body>
  </xsl:template>

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h2>
         Beth 
         
         Anderson
         
      </h2>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Rhapsodic. Passionate. Available on CD 
               <cite>
                  <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/" shape="rect">
                     Two by Three
                  </a>
               </cite> 
               from North/South Consonance (1998).
            </p>
            
         </description>
      </p>
      <h2>
         Linda 
         
         Bouchard
         
      </h2>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
      </ul>
      <p>
         <description>
            <p>Arrangement from Propos</p>
         </description>
      </p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
      </ul>
      <p></p>
      <h2>
         Julie 
         
         Mandel
         
      </h2>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         <description>
            
            <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
               Christine Ims, and Susan Jolles. In 3 movements :
            </p>
            
            <ul>
               
               <li>mvt. 1: 5:01</li>
               
               <li>mvt. 2: 4:11</li>
               
               <li>mvt. 3: 4:26</li>
               
            </ul>  
            
         </description>
      </p>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li>fl, pn</li>
      </ul>
      <p>
         <description>
            <p>3 movements</p>
         </description>
      </p>
      <h2>
         Margaret 
         De 
         Wys
         
      </h2>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Commissioned as quartet for the Meridian String Quartet. 
               Sonorous, bold. Moderate difficulty. Tape available.
            </p>
            
         </description>
      </p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.elharo.com/">
         Elliotte 
         Rusty 
         Harold
         
      </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

Sorting by Composition Title

Sorting by composition title is equally straight-forward but we have to do it in a separate xsl:apply-templates element

  <xsl:template match="catalog">
    <head>
       <title><xsl:value-of select="category"/></title>      
    </head>
    <body>
       <h1><xsl:value-of select="category"/></h1>      
       <xsl:apply-templates select="composer">
         <xsl:sort select="name/last_name"/>
         <xsl:sort select="name/first_name"/>
         <xsl:sort select="name/middle_name"/>
       </xsl:apply-templates>
       <hr/>
       Copyright <xsl:value-of select="copyright"/><br/>
       Last Modified: <xsl:value-of select="last_updated"/><br/>
       <xsl:apply-templates select="maintainer"/>
    </body>
  </xsl:template>
  
  <xsl:template match="composer">
    <h2><xsl:value-of select="name"/></h2>
    <xsl:apply-templates select="../composition[@composer=current()/@id]">
       <xsl:sort select="title"/>      
    </xsl:apply-templates>
  </xsl:template>

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <h2>
         Beth 
         
         Anderson
         
      </h2>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Rhapsodic. Passionate. Available on CD 
               <cite>
                  <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/" shape="rect">
                     Two by Three
                  </a>
               </cite> 
               from North/South Consonance (1998).
            </p>
            
         </description>
      </p>
      <h2>
         Linda 
         
         Bouchard
         
      </h2>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
      </ul>
      <p>
         <description>
            <p>Arrangement from Propos</p>
         </description>
      </p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
      </ul>
      <p></p>
      <h2>
         Julie 
         
         Mandel
         
      </h2>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li>fl, pn</li>
      </ul>
      <p>
         <description>
            <p>3 movements</p>
         </description>
      </p>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         <description>
            
            <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
               Christine Ims, and Susan Jolles. In 3 movements :
            </p>
            
            <ul>
               
               <li>mvt. 1: 5:01</li>
               
               <li>mvt. 2: 4:11</li>
               
               <li>mvt. 3: 4:26</li>
               
            </ul>  
            
         </description>
      </p>
      <h2>
         Margaret 
         De 
         Wys
         
      </h2>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Commissioned as quartet for the Meridian String Quartet. 
               Sonorous, bold. Moderate difficulty. Tape available.
            </p>
            
         </description>
      </p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.elharo.com/">
         Elliotte 
         Rusty 
         Harold
         
      </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

xsl:for-each

  <xsl:template match="catalog">
    <head>
       <title><xsl:value-of select="category"/></title>      
    </head>
    <body>
       <!-- Header -->            
       <h1><xsl:value-of select="category"/></h1>
       <ul>
         <xsl:for-each select="composition">
           <li><xsl:value-of select="title"/></li>
         </xsl:for-each>
       </ul>
       
       <!-- Body -->            
       <xsl:apply-templates select="composer">
         <xsl:sort select="name/last_name"/>
         <xsl:sort select="name/first_name"/>
         <xsl:sort select="name/middle_name"/>
       </xsl:apply-templates>
       
       <!-- Signature -->      
       <hr/>
       Copyright <xsl:value-of select="copyright"/><br/>
       Last Modified: <xsl:value-of select="last_updated"/><br/>
       <xsl:apply-templates select="maintainer"/>
    </body>
  </xsl:template>

• . selects the context node

• xsl:for-each iterates through the selected nodes, setting each one to the current node in turn but does not apply templates to that node.

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <ul>
         <li>Trio for Flute, Viola and Harp</li>
         <li>Charmonium</li>
         <li>Invention for Flute and Piano</li>
         <li>Little Trio</li>
         <li>Dr. Blood's Mermaid Lullaby</li>
         <li>Trio: Dream in D</li>
         <li>Propos II</li>
         <li>Rictus En Mirroir</li>
      </ul>
      <h2>
         Beth 
         
         Anderson
         
      </h2>
      <h3>Dr. Blood's Mermaid Lullaby</h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Little Trio</h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>Trio: Dream in D</h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Rhapsodic. Passionate. Available on CD 
               <cite>
                  <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/" shape="rect">
                     Two by Three
                  </a>
               </cite> 
               from North/South Consonance (1998).
            </p>
            
         </description>
      </p>
      <h2>
         Linda 
         
         Bouchard
         
      </h2>
      <h3>Propos II</h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
      </ul>
      <p>
         <description>
            <p>Arrangement from Propos</p>
         </description>
      </p>
      <h3>Rictus En Mirroir</h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
      </ul>
      <p></p>
      <h2>
         Julie 
         
         Mandel
         
      </h2>
      <h3>Invention for Flute and Piano</h3>
      <ul>
         <li>1994</li>
         <li>fl, pn</li>
      </ul>
      <p>
         <description>
            <p>3 movements</p>
         </description>
      </p>
      <h3>Trio for Flute, Viola and Harp</h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         <description>
            
            <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
               Christine Ims, and Susan Jolles. In 3 movements :
            </p>
            
            <ul>
               
               <li>mvt. 1: 5:01</li>
               
               <li>mvt. 2: 4:11</li>
               
               <li>mvt. 3: 4:26</li>
               
            </ul>  
            
         </description>
      </p>
      <h2>
         Margaret 
         De 
         Wys
         
      </h2>
      <h3>Charmonium</h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Commissioned as quartet for the Meridian String Quartet. 
               Sonorous, bold. Moderate difficulty. Tape available.
            </p>
            
         </description>
      </p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.elharo.com/">
         Elliotte 
         Rusty 
         Harold
         
      </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

Sorting the Table of Contents

xsl:for-each can have an xsl:sort child just like xsl:apply-templates

  <xsl:template match="catalog">
    <head>
       <title><xsl:value-of select="category"/></title>      
    </head>
    <body>
       <!-- Header -->            
       <h1><xsl:value-of select="category"/></h1>
       <ul>
         <xsl:for-each select="composition">
           <xsl:sort select="title"/>
           <li><xsl:value-of select="title"/></li>
         </xsl:for-each>
       </ul>
       
       <!-- Body -->            
       <xsl:apply-templates select="composer">
         <xsl:sort select="name/last_name"/>
         <xsl:sort select="name/first_name"/>
         <xsl:sort select="name/middle_name"/>
       </xsl:apply-templates>
       
       <!-- Signature -->      
       <hr/>
       Copyright <xsl:value-of select="copyright"/><br/>
       Last Modified: <xsl:value-of select="last_updated"/><br/>
       <xsl:apply-templates select="maintainer"/>
    </body>
  </xsl:template>

Adding Links from the Table of Contents

• We need to add <a name="some_name">title</a> around each composition title so we have something to link to.

• The generate-id() function will choose a unique ID for a particular element.

Here's the new template for the composition

  <xsl:template match="composition">
    <h3>
      <a name="{generate-id()}">
        <xsl:value-of select="title"/>
      </a>
    </h3>

    <ul>
     <xsl:if test="date)">
       <li><xsl:value-of select="date"/></li>
     </xsl:if>
     <xsl:if test="string(length)">
       <li><xsl:value-of select="length"/></li>
     </xsl:if>
     <xsl:if test="string(instruments)">
       <li><xsl:value-of select="instruments"/></li>
     </xsl:if>
     <xsl:if test="string(publisher)">
       <li><xsl:value-of select="publisher"/></li>
     </xsl:if>    
    </ul>

    <p><xsl:apply-templates select="description"/></p>    
    
  </xsl:template>

Here's the new template for the tabel of contents link

   <xsl:template match="catalog">
    <head>
       <title><xsl:value-of select="category"/></title>      
    </head>
    <body>
       <!-- Header -->            
       <h1><xsl:value-of select="category"/></h1>
       <ul>
         <xsl:for-each select="composition">
           <xsl:sort select="title"/>
           <li>
             <a href="#{generate-id()}">
               <xsl:value-of select="title"/>
             </a>
           </li>
         </xsl:for-each>
       </ul>
       
       <!-- Body -->            
       <xsl:apply-templates select="composer">
         <xsl:sort select="name/last_name"/>
         <xsl:sort select="name/first_name"/>
         <xsl:sort select="name/middle_name"/>
       </xsl:apply-templates>
       
       <!-- Signature -->      
       <hr/>
       Copyright <xsl:value-of select="copyright"/><br/>
       Last Modified: <xsl:value-of select="last_updated"/><br/>
       <xsl:apply-templates select="maintainer"/>
    </body>
  </xsl:template> 

Although the ID is generated in two separate places, it is generated for the same node. Consequently, they are the same.

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <ul>
         <li><a href="#b1ac21">Charmonium</a></li>
         <li><a href="#b1ac27">Dr. Blood's Mermaid Lullaby</a></li>
         <li><a href="#b1ac23">Invention for Flute and Piano</a></li>
         <li><a href="#b1ac25">Little Trio</a></li>
         <li><a href="#b1ac31">Propos II</a></li>
         <li><a href="#b1ac33">Rictus En Mirroir</a></li>
         <li><a href="#b1ac19">Trio for Flute, Viola and Harp</a></li>
         <li><a href="#b1ac29">Trio: Dream in D</a></li>
      </ul>
      <h2>
         Beth 
         
         Anderson
         
      </h2>
      <h3><a name="b1ac27">Dr. Blood's Mermaid Lullaby</a></h3>
      <ul>
         <li>1980</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3><a name="b1ac25">Little Trio</a></h3>
      <ul>
         <li>1984</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3><a name="b1ac29">Trio: Dream in D</a></h3>
      <ul>
         <li>1980</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Rhapsodic. Passionate. Available on CD 
               <cite>
                  <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/" shape="rect">
                     Two by Three
                  </a>
               </cite> 
               from North/South Consonance (1998).
            </p>
            
         </description>
      </p>
      <h2>
         Linda 
         
         Bouchard
         
      </h2>
      <h3><a name="b1ac31">Propos II</a></h3>
      <ul>
         <li>1985</li>
         <li>11'</li>
         <li>2 tpt</li>
      </ul>
      <p>
         <description>
            <p>Arrangement from Propos</p>
         </description>
      </p>
      <h3><a name="b1ac33">Rictus En Mirroir</a></h3>
      <ul>
         <li>1985</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
      </ul>
      <p></p>
      <h2>
         Julie 
         
         Mandel
         
      </h2>
      <h3><a name="b1ac23">Invention for Flute and Piano</a></h3>
      <ul>
         <li>1994</li>
         <li>fl, pn</li>
      </ul>
      <p>
         <description>
            <p>3 movements</p>
         </description>
      </p>
      <h3><a name="b1ac19">Trio for Flute, Viola and Harp</a></h3>
      <ul>
         <li>1994</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         <description>
            
            <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
               Christine Ims, and Susan Jolles. In 3 movements :
            </p>
            
            <ul>
               
               <li>mvt. 1: 5:01</li>
               
               <li>mvt. 2: 4:11</li>
               
               <li>mvt. 3: 4:26</li>
               
            </ul>  
            
         </description>
      </p>
      <h2>
         Margaret 
         De 
         Wys
         
      </h2>
      <h3><a name="b1ac21">Charmonium</a></h3>
      <ul>
         <li>1991</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Commissioned as quartet for the Meridian String Quartet. 
               Sonorous, bold. Moderate difficulty. Tape available.
            </p>
            
         </description>
      </p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.elharo.com/">
         Elliotte 
         Rusty 
         Harold
         
      </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

Numbering Output

• The xsl:number element has a variety of attributes to determine number style, exactly what's counted, where numbering starts, and so forth

• The position() function returns the position of the current node in the context node list

  <xsl:template match="composition">
    <h3><xsl:number value="position()"/>.
      <a name="{generate-id()}">
        <xsl:value-of select="title"/>
      </a>
    </h3>

    <ul>
     <xsl:if test="date">
       <li><xsl:value-of select="date"/></li>
     </xsl:if>
     <xsl:if test="length">
       <li><xsl:value-of select="length"/></li>
     </xsl:if>
     <xsl:if test="instruments">
       <li><xsl:value-of select="instruments"/></li>
     </xsl:if>
     <xsl:if test="publisher">
       <li><xsl:value-of select="publisher"/></li>
     </xsl:if>    
    </ul>

    <p><xsl:apply-templates select="description"/></p>    
    
  </xsl:template>

String functions

• XPath has a number of basic functions for working with strings:

  • starts-with(main_string, prefix_string)

  • contains(containing_string, contained_string)

  • substring(string, offset, length)

  • substring-before(string, marker-string)

  • substring-after(string, marker-string)

  • string-length(string)

  • normalize(string)

  • translate(string, replaced_text, replacement_text)

  • concat(string1, string2, ...)

• The strings these operate on are generally the values of nodes

• These may be part of any select expression, but are most commonly used in xsl:value-of.

• XPath does not, however, provide full Perl or POSIX regular expressions.

• XSLT/XPath 2.0 might add these

substring()

• substring(string, offset, length)

• 1 is the first character

• length is optional

• Node-sets are automatically converted to their values

  <xsl:template match="composition">
    <h3><xsl:number value="position()"/>.
      <a name="{generate-id()}">
        <xsl:value-of select="title"/>
      </a>
    </h3>

    <ul>
     <xsl:if test="date">
       <!--not Y10K safe! -->
       <li><xsl:value-of select="substring(date,2,4)"/></li>
     </xsl:if>
     <xsl:if test="length">
       <li><xsl:value-of select="length"/></li>
     </xsl:if>
     <xsl:if test="instruments">
       <li><xsl:value-of select="instruments"/></li>
     </xsl:if>
     <xsl:if test="publisher">
       <li><xsl:value-of select="publisher"/></li>
     </xsl:if>    
    </ul>

    <p><xsl:apply-templates select="description"/></p>    
    
  </xsl:template>

The actual HTML output

<html>
   <head>
      <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
   
      <title>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </title>
   </head>
   <body>
      <h1>
         Small chamber ensembles - 2-4 Players by New York Women Composers
         
      </h1>
      <ul>
         <li><a href="#d1e139">Charmonium</a></li>
         <li><a href="#d1e197">Dr. Blood's Mermaid Lullaby</a></li>
         <li><a href="#d1e161">Invention for Flute and Piano</a></li>
         <li><a href="#d1e178">Little Trio</a></li>
         <li><a href="#d1e243">Propos II</a></li>
         <li><a href="#d1e263">Rictus En Mirroir</a></li>
         <li><a href="#d1e102">Trio for Flute, Viola and Harp</a></li>
         <li><a href="#d1e216">Trio: Dream in D</a></li>
      </ul>
      <h2>
         Beth 
          
         Anderson
         
      </h2>
      <h3>1.
         <a name="d1e197">Dr. Blood's Mermaid Lullaby</a></h3>
      <ul>
         <li>80</li>
         <li>3'</li>
         <li>fl or ob, or vn, or vc, pn</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>2.
         <a name="d1e178">Little Trio</a></h3>
      <ul>
         <li>84</li>
         <li>4'</li>
         <li>fl, guit, va</li>
         <li>ACA</li>
      </ul>
      <p></p>
      <h3>3.
         <a name="d1e216">Trio: Dream in D</a></h3>
      <ul>
         <li>80</li>
         <li>10'</li>
         <li>fl, pn, vc, or vn, pn, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Rhapsodic. Passionate. Available on CD 
               <cite>
                  <a href="http://www.amazon.com/exec/obidos/ASIN/B000007NMH/qid=913265342/sr=1-2/" shape="rect">
                     Two by Three</a></cite> 
               from North/South Consonance (1998).
            </p>
            
         </description>
      </p>
      <h2>
         Linda 
          
         Bouchard
         
      </h2>
      <h3>1.
         <a name="d1e243">Propos II</a></h3>
      <ul>
         <li>85</li>
         <li>11'</li>
         <li>2 tpt</li>
      </ul>
      <p>
         <description>
            <p>Arrangement from Propos</p>
         </description>
      </p>
      <h3>2.
         <a name="d1e263">Rictus En Mirroir</a></h3>
      <ul>
         <li>85</li>
         <li>14'</li>
         <li>fl, ob, hpschd, vc</li>
      </ul>
      <p></p>
      <h2>
         Julie 
          
         Mandel
         
      </h2>
      <h3>1.
         <a name="d1e161">Invention for Flute and Piano</a></h3>
      <ul>
         <li>94</li>
         <li>fl, pn</li>
      </ul>
      <p>
         <description>
            <p>3 movements</p>
         </description>
      </p>
      <h3>2.
         <a name="d1e102">Trio for Flute, Viola and Harp</a></h3>
      <ul>
         <li>94</li>
         <li>13'38"</li>
         <li>fl, hp, vla</li>
         <li>Theodore Presser</li>
      </ul>
      <p>
         <description>
            
            <p>Premiered at Queens College in April, 1996 by Sue Ann Kahn, 
               Christine Ims, and Susan Jolles. In 3 movements :
            </p>
            
            <ul>
               
               <li>mvt. 1: 5:01</li>
               
               <li>mvt. 2: 4:11</li>
               
               <li>mvt. 3: 4:26</li>
               
            </ul>  
            
         </description>
      </p>
      <h2>
         Margaret 
         De 
         Wys
         
      </h2>
      <h3>1.
         <a name="d1e139">Charmonium</a></h3>
      <ul>
         <li>91</li>
         <li>9'</li>
         <li>2 vln, vla, vc</li>
      </ul>
      <p>
         <description>
            
            <p>Commissioned as quartet for the Meridian String Quartet. 
               Sonorous, bold. Moderate difficulty. Tape available.
            </p>
            
         </description>
      </p>
      <hr>
      Copyright 1999 New York Women Composers<br>
      Last Modified: July 28, 1999<br><a href="http://www.elharo.com/">
         Elliotte 
         Rusty 
         Harold
         </a><br><a href="mailto:elharo@metalab.unc.edu">elharo@metalab.unc.edu</a></body>
</html>

Number Operators

• XPath has several operators for doing arithmetic:

  • +

  • -

  • *

  • div

  • mod

• These may be part of any select expression, but are most commonly used in predicates with comparison operators.

Number Functions

XPath includes five functions that operate on numbers:

• floor(number) returns the greatest integer smaller than the number

• ceiling(number) returns the smallest integer greater than the number

• round(number) rounds the number to the nearest integer

• sum(number) returns the sum of its arguments

• format-number(number, format-string) returns the string form of a number formatted according to the specified format-string as if by Java 1.1's java.text.DecimalFormat class

Where Does the Transformation Happen?

There are three primary ways XML documents are transformed into other formats, such as HTML, with an XSLT style sheet:

• The XML document and associated style sheet are both served to the client (Web browser), which then transforms the document as specified by the style sheet and presents it to the user.

• The server applies an XSL style sheet to an XML document to transform it to some other format (generally HTML) and sends the transformed document to the client (Web browser).

• A third program transforms the original XML document into some other format (often HTML) before the document is placed on the server. Both server and client only deal with the post-transform document.

Client Side Processing

• Place an xml-stylesheet processing instruction in the prolog immediately after the XML declaration (if any) and before the document type declaration (if any).

• This processing instruction should have a type attribute with the value text/xml and an href attribute whose value is an absolute or relative URL pointing to the style sheet.

<?xml version="1.0"?>
<?xml-stylesheet type="text/xml" href="compositions.xsl"?>

• Eventually application/xml+xslt will replace text/xml.

• IE uses the non-existent MIME media type text/xsl instead.

• This is also how you attach a CSS style sheet to a document. The only difference here is that the type attribute has the value text/xml instead of text/css.

A style sheet that works with Internet Explorer 5.0 and 5.5

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl">

  <xsl:template match="/">
    <html>
      <xsl:apply-templates select="catalog"/>
    </html>
  </xsl:template>

  <xsl:template match="catalog">
    <body>
      <xsl:apply-templates select="composition"/>
    </body>
  </xsl:template>

  <xsl:template match="composition">
    <h3><xsl:value-of select="name"/></h3>
  </xsl:template>

</xsl:stylesheet>

What else does XSLT have?

• Many more ways to select and match elements including descendants, attributes, comments, processing instructions, and text.

• Many more tests for predicates

• The xsl:element, xsl:attribute, xsl:processing-instruction, xsl:comment, and xsl:text elements can output elements, attributes, processing instructions, comments, and text calculated from data in the input document.

• The xsl:copy-of element to copy nodes from the input to the output with their contents intact

• Parameters for passing arguments to templates

• Modes for reprocessing the same element in a different fashion

• Recursion

• The xsl:variable element defines named constants that can clarify your code.

• Named templates, variables, and attribute sets help you reuse common template code.

• The xsl:choose and xsl:when elements let you select one of several possibilities depending on a condition.

• The xsl:import and xsl:include elements merge rules from different style sheets.

• Various attributes of the xsl:output element allow you to specify the output document's format, XML declaration, document type declaration, indentation, encoding and MIME type.

• Extension functions written in other languages like Java, JavaScript, and C++

• Extension elements written in other languages like Java, JavaScript, and C++

What does XSLT not have?

• A general regular expression language

• Non-final variables (hence no side effects)

• Loops

Summary

• The Extensible Stylesheet Language (XSL) comprises two separate XML applications for transforming and formatting XML documents.

• An XSL transformation applies rules to a tree read from an XML document to transform it into an output tree written as an XML document.

• An XSL template rule is an xsl:template element with a match attribute. Nodes in the input tree are compared against the patterns of the match attributes of the different template elements. When a match is found, the contents of the template are output.

• The value of a node is a pure text (no markup) string containing the contents of the node. This can be calculated by the xsl:value-of element.

• The xsl:apply-templates element continues processing the children of the current node

• The xsl:if element produces output if, and only if, its test attribute is true.

• The xsl:number element inserts the number specified by its value attribute into the output using a specified number format given by the format attribute.

• The xsl:sort element can reorder the input nodes before copying them to the output.

To Learn More

• The XML Bible, 2nd edition

  • Elliotte Rusty Harold

  • IDG Books, 2001

  • ISBN: 0-7645-4760-7

  • Chapter 17, XSLT: http://www.cafeconleche.org/books/bible2/chapters/ch18.html

  
  

• XML in a Nutshell

  • Elliotte Rusty Harold and W. Scott Means

  • O'Reilly & Associates, 2001

  • ISBN 0-596-00058-8

  • Chapter 9 XPath: http://www.oreilly.com/catalog/xmlnut/chapter/ch09.html

  
  

• XSL Transformations 1.0 Specification: http://www.w3.org/TR/xslt/

• XPath Specification: http://www.w3.org/TR/xpath

Part V: XML and Databases

until someone comes up with a language with simple SELECT-DELETE-UPDATE semantics, XML databases will be the OODBMSs of the new millenium. I remember being introduced to XML and thinking that the concepts behind relational databases were more complex than those behind the hierarchical structures that encompass XML, amazingly enough the W3C has proved me wrong by producing increasingly complex languages that supposedly deal with handling XML in databases yet have much less functionality than a simple language like SQL.

--Dare Obasanjo on the xml-dev mailing list

Don't drink the snake oil!

• XML is not a database, or a replacement for one.

• Out of the box, XML doesn't know anything SQL; SQL doesn't know anything aobut XML.

• But XML works very well with databases

• You generally have to provide the integration code yourself, but this is not hard.

• There are some third-party products and database add-ons that will do a lot of the work for you.

Integrating XML with Databases

• Two approaches:

1. Store the document as a field

2. Store pieces of the document as fields

Middleware

• There are a lot of products that will pull data out of a database and format it as XML:

  • Stonebroom's ASP2XML

  • Transparency's Beanstalk

  • IBM's DatabaseDom

  • infoteria's iConnector

  • IBM's DB2 XML Extender

  • FileMaker Web Companion

  • Oracle XML SQL Utility for Java

  • etc.

• Or roll your own:

  • Java + JDBC

  • PHP

  • ASP

  • Visual Basic

  • etc.

Database Exchange and Integration

• XML is a very convenient format to move data between systems

• It's all text; very platform independent.

• Field and record boundaries are very clear

• Schemas and DTDs can prevent you from accepting bad data

XQuery

Part VI: Programming with XML

XML (1.0 or 1.1 as presently conceived) is far from perfect as a serialization format for objects or binary data. BUT once the data is in XML, it is (in principle) liberated from the application or class definitions that produced it. One might think of some SOAP message as a kludgy serialization of some business object, but for others it's an XML "document" that they can whack on with XPath/XQuery/XSLT/SAX/DOM/RDF/godonlyknowswhat. THAT's the real power of XML as an object serialization format, and this totally overwhelms its limitations ... at least today. If someday there are cheap, ubiquitous ASN.1 tools for parsing, transformation, manipulation, display, and querying, then this advantage of XML goes away, and we'll be arguing about this on ASN-DEV or whatever.

--Mike Champion on the xml-dev mailing list

Language Choice

• Java works best

• C, Perl, Python etc. can also be used

• Unicode support is the biggest issue

Several APIs to choose from

• SAX

• DOM

• JDOM

• dom4j

• Parser specific APIs

SAX

• Public domain, developed on xml-dev mailing list

• Maintained by David Megginson

• org.xml.sax package

• Parser independent; programs can plug in different parsers

• http://www.megginson.com/SAX/

• Event based; the parser pushes data to your handler

• Read-only

• SAX omits DTD declarations

SAX2

• Adds:

  • Namespace support

  • Optional validation

  • Optional lexical events for comments, CDATA sections, entity references

• A lot more configurable

• Deprecates a lot of SAX1

• Adapter classes convert between SAX2 and SAX1 parsers.

The SAX Process

• Build a parser-specific implementation of the XMLReader interface using XMLReaderFactory

• Your code registers a ContentHandler with the parser

• An InputSource feeds the document into the parser

• As the document is read, the parser calls back to the methods of the ContentHandler to tell it what it's seeing in the document.

Parsing a Document with XMLReader

import org.xml.sax.*;
import org.xml.sax.helpers.*;
import java.io.*;


public class SAX2Checker {

  public static void main(String[] args) {
    
    if (args.length == 0) {
      System.out.println("Usage: java SAX2Checker URL1 URL2..."); 
    } 
    
    // set up the parser 
    XMLReader parser;
    try {
      parser = XMLReaderFactory.createXMLReader();
    } 
    catch (SAXException e) {
      try {
        parser = XMLReaderFactory.createXMLReader("org.apache.xerces.parsers.SAXParser");
      }
      catch (SAXException e2) {
        System.err.println("Error: could not locate a parser.");
        return;
      }
    }
     
    // start parsing... 
    for (int i = 0; i < args.length; i++) {
      
      // command line should offer URIs or file names
      try {
        parser.parse(args[i]);
        // If there are no well-formedness errors
        // then no exception is thrown
        System.out.println(args[i] + " is well formed.");
      }
      catch (SAXParseException e) { // well-formedness error
        System.out.println(args[i] + " is not well formed.");
        System.out.println(e.getMessage()
         + " at line " + e.getLineNumber() 
         + ", column " + e.getColumnNumber());
      }
      catch (SAXException e) { // some other kind of error
        System.out.println(e.getMessage());
      }
      catch (IOException e) {
        System.out.println("Could not check " + args[i] 
         + " because of the IOException " + e);
      }
      
    }  
  
  }

}

The ContentHandler interface

package org.xml.sax;


public interface ContentHandler {

    public void setDocumentLocator(Locator locator);
    
    public void startDocument() throws SAXException;
    
    public void endDocument()	throws SAXException;
    
    public void startPrefixMapping(String prefix, String uri) 
     throws SAXException;

    public void endPrefixMapping(String prefix) throws SAXException;

    public void startElement(String namespaceURI, String localName,
		 String qualifiedName, Attributes atts) throws SAXException;

    public void endElement(String namespaceURI, String localName,
     String rawName) throws SAXException;

    public void characters(char[] text, int start, int length) 
     throws SAXException;

    public void ignorableWhitespace(char[] text, int start, int length)
     throws SAXException;

    public void processingInstruction(String target, String data)
     throws SAXException;

    public void skippedEntity(String name) throws SAXException;
     
}

SAX Example

import org.apache.xerces.parsers.*;
import org.w3c.dom.*;
import org.xml.sax.*;
import java.io.IOException;
import java.util.StringTokenizer;


public class SAXWordCount implements ContentHandler {

  private int numWords;
    
  public void startDocument() throws SAXException {
    this.numWords = 0; 
  }

  public void endDocument() throws SAXException {
    System.out.println(numWords + " words");
    System.out.flush();
  }
  
  private StringBuffer sb = new StringBuffer();
  
  public void characters(char[] text, int start, int length) 
   throws SAXException {
    
    sb.append(text, start, length);
    
  }
  
  private void flush() {
    numWords += countWords(sb.toString());
    sb = new StringBuffer();    
  }
  
  // methods that signify a word break
  public void startElement(String namespaceURI, String localName,
	 String rawName, Attributes atts) throws SAXException {
    this.flush(); 
  }
  
  public void endElement(String namespaceURI, String localName,
	 String rawName) throws SAXException {
    this.flush(); 
  }
  
  public void processingInstruction(String target, String data)
   throws SAXException {
    this.flush(); 
  }

  // methods that aren't necessary in this example
  public void startPrefixMapping(String prefix, String uri) 
   throws SAXException {
    // ignore; 
  }

  public void ignorableWhitespace(char[] text, int start, int length)
   throws SAXException {
    // ignore; 
  }
  
  public void endPrefixMapping(String prefix) throws SAXException {
    // ignore; 
  }

  public void skippedEntity(String name) throws SAXException {
    // ignore; 
  }   
  
  public void setDocumentLocator(Locator locator) {}

  private static int countWords(String s) {
    
    if (s == null) return 0;
    s = s.trim();
    if (s.length() == 0) return 0;
    
    StringTokenizer st = new StringTokenizer(s);
    return st.countTokens();
    
  } 

  public static void main(String[] args) {
     
    SAXParser parser = new SAXParser();
    SAXWordCount counter = new SAXWordCount();
    parser.setContentHandler(counter);
    
    for (int i = 0; i < args.length; i++) {
      try {
        parser.parse(args[i]); 
      }
      catch (SAXException e) {
        System.err.println(e); 
      }
      catch (IOException e) {
        System.err.println(e); 
      }
      
    }
  
  } // end main

}

% java SAXWordCount hotcop.xml
16 words

Event Based API Caveats

• You do not always have all the information you need at the time of a given callback

• You may need to store information in various data structures (stacks, queues,vectors, arrays, etc.) and act on it at a later point

• For example, the characters() method is not guaranteed to give you the maximum number of contiguous characters. It may split a single run of characters over multiple method calls.

Document Object Model

• Defines how XML and HTML documents are represented as objects in programs

• W3C Standard

• Defined in IDL; thus language independent

• HTML as well as XML

• Writing as well as reading

• More complete than SAX or JDOM; covers everything except internal and external DTD subsets

• DOM focuses more on the document; SAX focuses more on the parser.

The Design of the DOM API

• Parser independent interfaces; parser dependent implementation classes. Most programs must use the parser dependent classes. JAXP helps solve this, but so far only for DOM Level 1.

• Everything's a Node:

  • Extensive use of polymorphism

  • Lots of casting

• Language independence means there's very limited use of the Java class library; Various features are reinvented

• Language independence requires no method overloading because not all languages support it.

• Several features are poor design in Java, if not in other languages:

  • Named constants are often shorts

  • Only one kind of exception; details provided by constants

  • No Java-specific utility methods like equals(), hashCode(), clone(), or toString()

DOM Evolution

• DOM Level 0

• DOM Level 1, a W3C Standard

• DOM Level 2, a W3C Standard

• DOM Level 3, several W3C Working Drafts

Eight Modules:

• Eight Modules:

  • Core: org.w3c.dom ^*

  • HTML: org.w3c.dom.html

  • Views: org.w3c.dom.views

  • StyleSheets: org.w3c.dom.stylesheets

  • CSS: org.w3c.dom.css

  • Events: org.w3c.dom.events ^*

  • Traversal: org.w3c.dom.traversal ^*

  • Range: org.w3c.dom.range

• Only the core and traversal modules really apply to XML. The other six are for HTML.

• ^* indicates Xerces support

DOM Trees

• Each XML document should is a tree.

• A tree contains nodes.

• Some nodes may contain other nodes (depending on node type).

• Each document node contains:

  • zero or one doctype nodes

  • one root element node

  • zero or more comment and processing instruction nodes

org.w3c.dom

• 17 interfaces:

  • Attr

  • CDATASection

  • CharacterData

  • Comment

  • Document

  • DocumentFragment

  • DocumentType

  • DOMImplementation

  • Element

  • Entity

  • EntityReference

  • NamedNodeMap

  • Node

  • NodeList

  • Notation

  • ProcessingInstruction

  • Text

• plus one exception: DOMException

• Plus a bunch of HTML stuff in org.w3c.dom.html and other packages

The DOM Process

• Library specific code creates a parser

• The parser parses the document and returns an org.w3c.dom.Document object.

• The entire document is stored in memory.

• DOM methods and interfaces are used to extract data from this object

Parsing documents with a DOM Parser Example

import org.apache.xerces.parsers.DOMParser;
import org.xml.sax.SAXException;
import java.io.IOException;
import org.w3c.dom.*;


public class DOMChecker {

  public static void main(String[] args) {
     
    // This is simpler but less flexible than the SAX approach.
    // Perhaps a good creational design pattern is needed here?   
  
    DOMParser parser = new DOMParser();
    
    for (int i = 0; i < args.length; i++) {
      try {
        // Read the entire document into memory
        parser.parse(args[i]); 
       
        Document d = parser.getDocument();
        // work with the document...
      }
      catch (SAXException e) {
        System.err.println(e); 
      }
      catch (IOException e) {
        System.err.println(e); 
      }
      
    }
  
  }

}

DOM Example

import org.apache.xerces.parsers.*;
import org.w3c.dom.*;
import org.xml.sax.*;
import java.io.IOException;
import java.util.StringTokenizer;


public class DOMWordCount {

  public static void main(String[] args) {
     
    DOMParser parser = new DOMParser();
    DOMWordCount counter = new DOMWordCount();
    
    for (int i = 0; i < args.length; i++) {
      try {
        // Read the entire document into memory
        parser.parse(args[i]); 
       
        Document d = parser.getDocument();
        int numWords = countWordsInNode(d);
        System.out.println(numWords + " words");

      }
      catch (SAXException e) {
        System.err.println(e); 
      }
      catch (IOException e) {
        System.err.println(e); 
      }
      
    }
  
  } // end main

  // note use of recursion
  public static int countWordsInNode(Node node) {
    
    int numWords = 0;
    
    if (node.hasChildNodes()) {
      NodeList children = node.getChildNodes();
      for (int i = 0; i < children.getLength(); i++) {
        numWords += countWordsInNode(children.item(i));
      } 
    }  

    int type = node.getNodeType();
    if (type == Node.TEXT_NODE) {
      String s = node.getNodeValue();
      numWords += countWordsInString(s);
    }
    
    return numWords;  
    
  }
  
  private static int countWordsInString(String s) {
    
    if (s == null) return 0;
    s = s.trim();
    if (s.length() == 0) return 0;
    
    StringTokenizer st = new StringTokenizer(s);
    return st.countTokens();
    
  } 

}

% java DOMWordCount hotcop.xml
16 words

JAXP, Java API for XML Processing

• JAXP 1.1 = SAX2 + DOM2 + TrAX + factory classes

• Factory classes are in the javax.xml.parsers

• Bundled with java 1.4 and later

JAXP Example

import javax.xml.parsers.*;
import org.w3c.dom.*;
import org.xml.sax.*;
import java.io.IOException;
import java.util.StringTokenizer;


public class JAXPWordCount {

  public static void main(String[] args) {
     
    try {
      DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
      DocumentBuilder parser = factory.newDocumentBuilder();
      JAXPWordCount counter = new JAXPWordCount();
    
      for (int i = 0; i < args.length; i++) {
        try {
          // Read the entire document into memory
          Document d = parser.parse(args[i]); 
          int numWords = countWordsInNode(d);
          System.out.println(numWords + " words");
        }
        catch (SAXException e) {
          System.err.println(e); 
        }
        catch (IOException e) {
          System.err.println(e); 
        }
      } // end for
    } // end try
    catch (ParserConfigurationException e) {
      System.err.println(
       "No parser suporting JAXP could be found in the local class path."); 
    }
  
  } // end main

  // note use of recursion
  public static int countWordsInNode(Node node) {
    
    int numWords = 0;
    
    if (node.hasChildNodes()) {
      NodeList children = node.getChildNodes();
      for (int i = 0; i < children.getLength(); i++) {
        numWords += countWordsInNode(children.item(i));
      } 
    }  

    int type = node.getNodeType();
    if (type == Node.TEXT_NODE) {
      String s = node.getNodeValue();
      numWords += countWordsInString(s);
    }
    
    return numWords;  
    
  }
  
  private static int countWordsInString(String s) {
    
    if (s == null) return 0;
    s = s.trim();
    if (s.length() == 0) return 0;
    
    StringTokenizer st = new StringTokenizer(s);
    return st.countTokens();
    
  } 

}

% java JAXPWordCount hotcop.xml
16 words

JDOM

• More Java like tree-based API

• Parser independent classes sit on top of parsers and other APIs

The JDOM Process

• Construct an org.jdom.input.SAXBuilder or an org.jdom.input.DOMBuilder

• Invoke the builder's build() method to build a Document object from a

  • Reader

  • InputStream

  • URL

  • File

  • SYSTEM ID String

• If there's a problem building the document, a JDOMException is thrown

• Work with the resulting Document object

Parsing a Document with JDOM

import org.jdom.JDOMException;
import org.jdom.input.SAXBuilder;


public class JDOMChecker {

  public static void main(String[] args) {
  
    if (args.length == 0) {
      System.out.println("Usage: java JDOMChecker URL1 URL2..."); 
    } 
      
    SAXBuilder builder = new SAXBuilder();
     
    // start parsing... 
    for (int i = 0; i < args.length; i++) {
      
      // command line should offer URIs or file names
      try {
        builder.build(args[i]);
        // If there are no well-formedness errors, 
        // then no exception is thrown
        System.out.println(args[i] + " is well formed.");
      }
      catch (JDOMException e) { // indicates a well-formedness or other error
        System.out.println(args[i] + " is not well formed.");
        System.out.println(e.getMessage());
      }
      
    }   
  
  }

}

Parser Results

% java JDOMChecker shortlogs.xml HelloJDOM.java
shortlogs.xml is well formed.
HelloJDOM.java is not well formed.
The markup in the document preceding the root element must be well-formed.: 
Error on line 1 of XML document: The markup in the document preceding the 
root element must be well-formed.

JDOM Example

import org.jdom.*;
import org.jdom.input.SAXBuilder;
import java.util.*;


public class JDOMWordCount {

  public static void main(String[] args) {
  
    if (args.length == 0) {
      System.out.println("Usage: java JDOMWordCount URL1 URL2..."); 
    } 
      
    SAXBuilder builder = new SAXBuilder();
     
    // start parsing... 
    for (int i = 0; i < args.length; i++) {
      
      // command line should offer URIs or file names
      try {
        Document doc = builder.build(args[i]);
        Element root = doc.getRootElement();
        int numWords = countWordsInElement(root);
        System.out.println(numWords + " words");

      }
      catch (JDOMException e) { // indicates a well-formedness or other error
        System.out.println(args[i] + " is not well formed.");
        System.out.println(e.getMessage());
      }
      
    }   
  
  }

  public static int countWordsInElement(Element element) {
    
    int numWords = 0;
    
    List children = element.getContent();
    Iterator iterator = children.iterator();
    while (iterator.hasNext()) {
      Object o = iterator.next();
      if (o instanceof Text) {
        numWords += countWordsInString((Text) o);
      } 
      else if (o instanceof Element) {
        // note use of recursion
        numWords += countWordsInElement((Element) o); 
      } 
    }
    
    return numWords;  
    
  }

  private static int countWordsInString(Text text) {
    
    if (text == null) return 0;
    String s = text.getText();
    s = s.trim();
    if (s.length() == 0) return 0;
    
    StringTokenizer st = new StringTokenizer(s);
    return st.countTokens();
    
  }

}

% java JDOMWordCount hotcop.xml
16 words

To Learn More

• This presentation: http://www.cafeconleche.org/slides/sd2002west/introxml

• XML in a Nutshell

  • Elliotte Rusty Harold and W. Scott Means

  • O'Reilly & Associates, 2001

  • ISBN 0-596-00058-8

  • XPath: http://www.oreilly.com/catalog/xmlnut/chapter/ch09.html

  
  

• XML Bible, second edition

  • Elliotte Rusty Harold

  • Hungry Minds, 2001

  • ISBN 0-7645-4760-7

  • XSLT: http://www.cafeconleche.org/books/bible2/chapters/18.html

  • XSL-FO: http://www.cafeconleche.org/books/bible2/chapters/19.html

  • XLinks: http://www.cafeconleche.org/books/bible2/chapters/20.html

  • XPointers: http://www.cafeconleche.org/books/bible2/chapters/21.html