XML Fundamentals

XML Fundamentals

Elliotte Rusty Harold

O'Reilly Enterprise Java Conference

March 26, 2001

elharo@metalab.unc.edu

http://www.ibiblio.org/xml/

Outline

Part I: XML Overview

What is XML?

XML is a Meta Markup Language

XML describes structure and semantics, not formatting

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

<?xml version="1.0">
<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 Sheets provide formatting

SONG     {display: block}
TITLE    {display: block; font-family: Helvetica, serif;
          font-size: 20pt; font-weight: bold}
COMPOSER {display: block; 
          font-family: Times, Times New Roman, serif;
          font-size: 14pt;
          font-style: italic}
ARTIST   {display: block; 
          font-family: Times, Times New Roman, serif;
          font-size: 14pt; font-weight: bold;
          font-style: italic}
PUBLISHER {display: block; 
           font-family: Times, Times New Roman, serif;
           font-size: 14pt}
LENGTH    {display: block; 
           font-family: Times, Times New Roman, serif;
           font-size: 14pt}
YEAR      {display: block; 
           font-family: Times, Times New Roman, serif;
           font-size: 14pt}

Attaching style sheets to documents

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

song.xsl

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

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

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

</xsl:stylesheet>

Applying an XSLT Style Sheet

Output

<html>
   <body>
      <h1>Hot Cop 
         by the 
         Village People
      </h1>
      <ul>
         <li>Composer: Jacques Morali</li>
         <li>Composer: Henri Belolo</li>
         <li>Composer: Victor Willis</li>
         <li>Publisher: PolyGram Records</li>
         <li>Year: 1978</li>
         <li>Producer: Jacques Morali</li>
      </ul>
   </body>
</html>
View in browser

Editing and Saving XML Documents

A More Complex Song Description in XML

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<?xml-stylesheet type="text/css" href="song.css"?>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <PHOTO SRC="hotcop.jpg" WIDTH="100" HEIGHT="200"
    ALT="Victor Willis in Cop Outfit"/>
  <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 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 -->

New features:

View Document in Browser

The XML Declaration

Attributes

Attributes vs. Elements

When not to use attributes

Part II: What is XML Good For?

What is XML used for?

Domain-Specific Markup Languages

Self-Describing Data

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

Can assemble data from multiple sources

XML Applications

Example XML Applications

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

Classic Literature

Vector Graphics

A VML document

The Resource Description Framework (RDF)

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.ibiblio.org/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

Schemas

W3C XML Schema Language Example

<?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:seq>
      <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:gYear" 
                   minOccurs="1" maxOccurs="1"/>

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

</xsd:schema>

XLinks

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

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

Part III: A Practical Example

A larger example: Music Catalog

Sample Catalog

http://www.ibiblio.org/nywc/
Offline version/

Organizing the Data

What is the Root Element

The Root Element

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

What are the Immediate Children of the Root?

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

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

Grand Children

<?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

Attributes

<?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

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

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

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>
View 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

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

<?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

A Style Sheet for the Music Catalog

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

Possible Solutions

CSS or XSL?

Part IV: Well-formedness

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

Character References

Part V: DTDs

Well-formedness vs validity

DTDs and Validity

What is a DTD?

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

A Valid Song Document

<?xml version="1.0"?>
<!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 sax.SAXCount -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.SAXCount -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>

The importance of validation

An Example Document

<?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>

  <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>

  <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>
      Commissioned as quartet for the Meridian String Quartet. 
      Sonorous, bold. Moderate difficulty. Tape available.
    </description> 
    <publisher></publisher>
  </composition>

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

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

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

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

</catalog>
View in Browser

Element Declarations

Content Specifications

ANY

<!ELEMENT catalog ANY>

#PCDATA content model

  <year>1984</year>

<!ELEMENT year (#PCDATA)>

Valid and Invalid #PCDATA

<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>

<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>

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

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

Child Elements

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

<!ELEMENT date (year)>

Child Elements

You only have to declare the immediate children

   <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>

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

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

Sequences

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

To use a sequence in an ELEMENT declaration

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>

<!ELEMENT cataloging_info (abstract, keyword+)>

Zero or More Children *

<!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>

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

Choices

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

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)>

Content Models You Can't Declare

Attribute Declarations

Recall this element:

  <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>

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.macfaq.com/personal.html">
    <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

#REQUIRED

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

#IMPLIED

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

#FIXED

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

Attribute Types

CDATA

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

ID

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

IDREF

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

IDREFS

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

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>

Part VI: Namespaces

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

Namespaces disambiguate elements

Namespace Syntax

Namespace URIs

Binding Prefixes to Namespace URIs

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

URIs matter; not prefixes

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

The Default Namespace

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>

Namespaces and DTDs

To Learn More

Index | Cafe con Leche
Copyright 2001 Elliotte Rusty Harold
elharo@metalab.unc.edu
Last Modified March 27, 2001