XML Fundamentals

Elliotte Rusty Harold

Bank of America

September 21, 2000

elharo@metalab.unc.edu

http://metalab.unc.edu/xml/

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

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 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>

View Document in Browser

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>

View Document in Browser

Editing and Saving XML Files

Plain ASCII or UTF-8 text
.xml is standard file extension
Any standard 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>

View Document in Browser

Style Sheet Languages

Cascading Style Sheets Level 1 (CSS1)
- Internet Explorer 5.0
- Mozilla 5.0
Cascading Style Sheets Level 2 (CSS2)
- Internet Explorer 5 (partial)
- Mozilla 5.0 (partial)
Extensible Stylesheet Language (XSL)
- Internet Explorer 5.0 (older draft, buggy)
- LotusXSL, XT, Xalan, Saxon, other non-browser converters
Document Style and Semantics Language (DSSSL)
- Jade

An XSLT stylesheet

<?xml version="1.0"?>
<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>
<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 -x org.apache.xerces.parsers.SAXParser xml_fundamentals.xml slides.xsl hotcop.xml song3.xsl <html> ...

View Document in Browser

Well-formedness

Rules:

Open and close all tags
Empty 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 entities
Only the five predefined entity references are used
Plus more...

Validity

To be valid an XML document must be

Well-formed
Must have a DTD
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.DOMCount -v validhotcop.xml
[Error] validhotcop.xml:13:9: The content of element type "SONG" must match "(TI
TLE,COMPOSER+,PRODUCER*,PUBLISHER*,LENGTH?,YEAR?)".
validhotcop.xml: 550 ms (10 elems, 0 attrs, 28 spaces, 98 chars)

A valid document:

% java dom.DOMCount -v validhotcop.xml
validhotcop.xml: 291 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
- 8859_1
- 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:
- Bad:

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

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://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>
  <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 & Associates</H1>
- Bad:
  <H1>O'Reilly & Associates</H1>
- Good:
  <CODE>for (int i = 0; i <= args.length; i++ ) { </CODE>
- Bad:
  <CODE>for (int i = 0; i <= args.length; i++ ) { </CODE>
Only the five predefined entity references are used
- Good:
- Bad:
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

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

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

Example XML Applications

Web Pages
Mathematical Equations
Music Notation
Vector Graphics
Metadata
and more...

Mathematical Markup Language

<?xml version="1.0"?>
<html xmlns="http://www.w3.org/TR/REC-html40"
      xmlns:m="http://www.w3.org/TR/REC-MathML/"
>
<head>
<title>Fiat Lux</title>
<meta name="GENERATOR" content="amaya V1.3b" />
</head>
<body>

<P>
And God said,
</P>

<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>
</math>

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

Channel Definition Format

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

Classic Literature

Vector Graphics

Vector Markup Language (VML)

Internet Explorer 5.0
Microsoft Office 2000

Scalable Vector Graphics (SVG)

A VML document

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://metalab.unc.edu/xml/>
    <dc:CREATOR>Elliotte Rusty Harold</dc:CREATOR>
    <dc:TITLE>Cafe con Leche</dc:TITLE>
  </rdf:Description>
</rdf:RDF>

XML for XML

XSL: The Extensible Stylesheet Language
XML Schema
XLinks: The Extensible Linking Language

XSL: The Extensible Stylesheet Language

XSLT: XSL Transformations
XSL-FO XSL Formatting Objects

W3C XML Schemas

An XML syntax to replace DTDs
Data typing of element and attribute content

<xsd:schema xmlns:xsd="http://www.w3.org/1999/XMLSchema">
 
  <xsd:element name="SONG" type="SongType"/>

  <xsd:complexType name="SongType">
  
    <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:timeDuration" minOccurs="0" maxOccurs="1"/>
    <xsd:element name="YEAR"   type="xsd:year" minOccurs="1" maxOccurs="1"/>

    <xsd:element name="ARTIST" type="xsd:string" minOccurs="1" maxOccurs="unbounded"/>
    
  </xsd:complexType>

</xsd:schema>

XLinks: The Extensible Linking Language

Any element can be a link
Links can be bi-directional
Links can be separated from the documents they connect

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

Non-XML for XML

XPath, the XML Path Language
XPointers
And 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

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

Microsoft Office 2000
Netscape What's Related

A larger XML example: Music Catalog

Examine the data
Design a vocabulary for the data
Write a style sheet

Sample Catalog

http://metalab.unc.edu/nywc/

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>

View in Browser

The Root Element Style Sheet

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

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

</xsl:stylesheet>

The Root Element Style Sheet Output

<html>
   <head>
      <meta http-equiv="Content-Type" content="application/xml; charset=utf-8">
   
      <title></title>
   </head>
   <body>
      Everything else will go here...
      
   </body>
</html>

View Result in Browser

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>

View in Browser

Style Sheet

<?xml version="1.0"?>
<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>  
      </body>
  </xsl:template>

</xsl:stylesheet>

Style Sheet 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>
   </body>
</html>

View Result in Browser

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>

View in Browser

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>

View in Browser

Style Sheet

<?xml version="1.0"?>
<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="composer"/> 
      </body>
  </xsl:template>

  <xsl:template match="composer">
      <h2><xsl:value-of select="."/></h2>
  </xsl:template>

</xsl:stylesheet>

Style Sheet 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>
      <h2>
         Margaret De Wys
         
      </h2>
      <h2>
         Beth Anderson
         
      </h2>
      <h2>
         Linda Bouchard
         
      </h2>
   </body>
</html>

View Result in Browser

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>

View in Browser

The Same Style Sheet Still Works

<?xml version="1.0"?>
<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="composer"/> 
      </body>
  </xsl:template>

  <xsl:template match="composer">
      <h2><xsl:value-of select="."/></h2>
  </xsl:template>

</xsl:stylesheet>

Style Sheet 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>
      <h2>
         
         Margaret 
         De 
         Wys
         
         
      </h2>
      <h2>
         
         Beth 
          
         Anderson
         
         
      </h2>
      <h2>
         
         Linda 
          
         Bouchard
         
         
      </h2>
   </body>
</html>

View Result in Browser

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>

View in Browser

Style Sheet with Attributes

<?xml version="1.0"?>
<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="composer"/> 
      </body>
  </xsl:template>

  <xsl:template match="composer">
      <h2 id="{@id}"><xsl:value-of select="."/></h2>
  </xsl:template>

</xsl:stylesheet>

Style Sheet 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 id="c1">
         
         Julie 
          
         Mandel
         
         
      </h2>
      <h2 id="c2">
         
         Margaret 
         De 
         Wys
         
         
      </h2>
      <h2 id="c3">
         
         Beth 
          
         Anderson
         
         
      </h2>
      <h2 id="c4">
         
         Linda 
          
         Bouchard
         
         
      </h2>
   </body>
</html>

View Result in Browser

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

Composition Example in HTML

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>

View in Browser

Style Rule for Compositions

<?xml version="1.0"?>
<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="composer"/> 
        <dl>
          <xsl:apply-templates select="composition"/> 
        </dl>
      </body>
  </xsl:template>

  <xsl:template match="composer">
    <h2 id="{@id}"><xsl:value-of select="."/></h2>
  </xsl:template>

  <xsl:template match="composition">
    <dt><cite><xsl:value-of select="title"/></cite> 
        (<xsl:value-of select="date"/>)
        <xsl:value-of select="length"/>
        <xsl:value-of select="instruments"/>
    </dt>
    <dd>
      <xsl:value-of select="description"/>
      <xsl:value-of select="publisher"/>
    </dd>
  </xsl:template>

</xsl:stylesheet>

Style Sheet 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 id="c1">
         
         Julie 
          
         Mandel
         
         
      </h2>
      <h2 id="c2">
         
         Margaret 
         De 
         Wys
         
         
      </h2>
      <h2 id="c3">
         
         Beth 
          
         Anderson
         
         
      </h2>
      <h2 id="c4">
         
         Linda 
          
         Bouchard
         
         
      </h2>
      <dl>
         <dt><cite>Trio for Flute, Viola and Harp</cite> 
            (1994)
            13'38"fl, hp, vla
         </dt>
         <dd>
            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
         </dd>
         <dt><cite>Charmonium</cite> 
            (1991)
            9'2 vln, vla, vc
         </dt>
         <dd>
            Commissioned as quartet for the Meridian String Quartet. 
            Sonorous, bold. Moderate difficulty. Tape available.
            
         </dd>
         <dt><cite>Invention for Flute and Piano</cite> 
            (1994)
            fl, pn
         </dt>
         <dd>3 movements</dd>
         <dt><cite>Little Trio</cite> 
            (1984)
            4'fl, guit, va
         </dt>
         <dd>ACA</dd>
         <dt><cite>Dr. Blood's Mermaid Lullaby</cite> 
            (1980)
            3'fl or ob, or vn, or vc, pn
         </dt>
         <dd>ACA</dd>
         <dt><cite>Trio: Dream in D</cite> 
            (1980)
            10'fl, pn, vc, or vn, pn, vc
         </dt>
         <dd>
            Rhapsodic. Passionate. Available on CD
            Two by Three from North/South Consonance (1998).
            
         </dd>
         <dt><cite>Propos II</cite> 
            (1985)
            11'2 tpt
         </dt>
         <dd>Arrangement from Propos</dd>
         <dt><cite>Rictus En Mirroir</cite> 
            (1985)
            14'fl, ob, hpschd, vc
         </dt>
         <dd></dd>
      </dl>
   </body>
</html>

View Result in Browser

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>

View in Browser

Arranging Compositions by Composer

<?xml version="1.0"?>
<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="composer"/> 

      </body>
  </xsl:template>

  <xsl:template match="composer">
    <h2 id="{@id}"><xsl:value-of select="."/></h2>
    <dl>
      <xsl:apply-templates select="../composition[@composer=current()/@id]"/> 
    </dl>
  </xsl:template>

  <xsl:template match="composition">
    <dt><cite><xsl:value-of select="title"/></cite> 
        (<xsl:value-of select="date"/>)
        <xsl:value-of select="length"/>
        <xsl:value-of select="instruments"/>
    </dt>
    <dd>
      <xsl:value-of select="description"/>
      <xsl:value-of select="publisher"/>
    </dd>
  </xsl:template>

</xsl:stylesheet>

Style Sheet 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 id="c1">
         
         Julie 
          
         Mandel
         
         
      </h2>
      <dl>
         <dt><cite>Trio for Flute, Viola and Harp</cite> 
            (1994)
            13'38"fl, hp, vla
         </dt>
         <dd>
            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
         </dd>
         <dt><cite>Invention for Flute and Piano</cite> 
            (1994)
            fl, pn
         </dt>
         <dd>3 movements</dd>
      </dl>
      <h2 id="c2">
         
         Margaret 
         De 
         Wys
         
         
      </h2>
      <dl>
         <dt><cite>Charmonium</cite> 
            (1991)
            9'2 vln, vla, vc
         </dt>
         <dd>
            Commissioned as quartet for the Meridian String Quartet. 
            Sonorous, bold. Moderate difficulty. Tape available.
            
         </dd>
      </dl>
      <h2 id="c3">
         
         Beth 
          
         Anderson
         
         
      </h2>
      <dl>
         <dt><cite>Little Trio</cite> 
            (1984)
            4'fl, guit, va
         </dt>
         <dd>ACA</dd>
         <dt><cite>Dr. Blood's Mermaid Lullaby</cite> 
            (1980)
            3'fl or ob, or vn, or vc, pn
         </dt>
         <dd>ACA</dd>
         <dt><cite>Trio: Dream in D</cite> 
            (1980)
            10'fl, pn, vc, or vn, pn, vc
         </dt>
         <dd>
            Rhapsodic. Passionate. Available on CD 
            Two by Three 
            from North/South Consonance (1998).
            
         </dd>
      </dl>
      <h2 id="c4">
         
         Linda 
          
         Bouchard
         
         
      </h2>
      <dl>
         <dt><cite>Propos II</cite> 
            (1985)
            11'2 tpt
         </dt>
         <dd>Arrangement from Propos</dd>
         <dt><cite>Rictus En Mirroir</cite> 
            (1985)
            14'fl, ob, hpschd, vc
         </dt>
         <dd></dd>
      </dl>
   </body>
</html>

View Result in Browser

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>

View in Browser

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.macfaq.com/personal.html">
    <name>
      <first_name>Elliotte</first_name> 
      <middle_name>Rusty</middle_name> 
      <last_name>Harold</last_name>
    </name>
  </maintainer>

</catalog>

View in Browser

Cascading Style Sheets

Partially supported by Mozilla and IE 5.0
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>

View in Browser

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 }

View in Browser

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 }

View in Browser

A style rule for the composer element

Make it look like a level 2 head
No need to styleize the first, middle, and last names separately

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

View in Browser

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}

View in Browser

A style rule for the catalog info

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

display: none requires CSS2:

View in Browser

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.macfaq.com/personal.html">
    <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

View in Browser

Style Rules for composition children

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

View in Browser

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

Programming with XML

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
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

Construct a parser-specific implementation of the XMLReader interface
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 methods of the ContentHandler to tell it what it's seeing in the document.

Making an XMLReader

The XMLReaderFactory.createXMLReader() method instantiates an XMLReader subclass named by the org.xml.sax.driver system property:
```
try {
  XMLReader parser = XMLReaderFactory.createXMLReader();
} 
catch (SAXException e) {
  System.err.println(e);
}
```

The XMLReaderFactory.createXMLReader(String className) method instantiates an XMLReader subclass named by its argument:

try {
  XMLReader parser 
   = XMLReaderFactory.createXMLReader("org.apache.xerces.parsers.SAXParser");
} 
catch (SAXException e) {
  System.err.println(e);
}

Or you can use the constructor in the package-specific class:
```
XMLReader parser = new SAXParser();
```

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 rawName, Attributes atts) throws SAXException;

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

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

    public void ignorableWhitespace(char ch[], 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

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

Entire document is represented as a grove of trees.
Each XML document should contain exactly one 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:

DOM Interface JDOM Equivalent

Attr Attribute

CDATASection

CharacterData

Comment Comment

Document Document

DocumentFragment

DocumentType DocType

DOMImplementation

Element Element

Entity Entity

EntityReference

NamedNodeMap

Node

NodeList

Notation

ProcessingInstruction ProcessingInstruction

Text

plus one exception: DOMException
Plus a bunch of HTML stuff in org.w3c.dom.html and other packages we will ignore

DOM Interface	JDOM Equivalent
`Attr`	`Attribute`
`CDATASection`
`CharacterData`
`Comment`	`Comment`
`Document`	`Document`
`DocumentFragment`
`DocumentType`	`DocType`
`DOMImplementation`
`Element`	`Element`
`Entity`	`Entity`
`EntityReference`
`NamedNodeMap`
`Node`
`NodeList`
`Notation`
`ProcessingInstruction`	`ProcessingInstruction`
`Text`

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

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.getMixedContent();
    Iterator iterator = children.iterator();
    while (iterator.hasNext()) {
      Object o = iterator.next();
      if (o instanceof String) {
        numWords += countWordsInString((String) o);
      } 
      else if (o instanceof Element) {
        // note use of recursion
        numWords += countWordsInElement((Element) o); 
      } 
    }
    
    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 JDOMWordCount hotcop.xml
16 words

Questions?

To Learn More

The XML Bible
Elliotte Rusty Harold
IDG Books, 1999
ISBN: 0-7645-3236-7

This presentation: http://metalab.unc.edu/xml/slides/bank_of_america/fundamentals/

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