Extensible Markup Language

Home

» XML BASICS HOME » XML Introduction » XML How to Use » XML Syntax » XML Attributes » XML Validation » XML in your Browser » XML Viewing » XML Display

» DTD HOME » DTD Introduction » DTD Elements » DTD Attributes » DTD Entities » DTD Validation » DTD Examples

» DOM HOME » DOM Introduction » DOM Parsing » DOM ParseError » DOM Access

» XSL HOME » XSL Introduction » XSL Transformation » XSL on the Client » XSL on the Server » XSL Sorting » XSL Filtering » XSL If..Then » XSL Choose

XML RSS XHTML XML Examples

» XML Links HOME » W3C Links » Microsoft » Netscape » Interesting Reading » XML Books

XML Forum ASP Information Technology Jobs

Search XML Files:

XML Files Updates

DEVELOPER CHANNEL
FlashKit.com
JavaScript.com
JavaScriptSource
Developer Jobs
ScriptSearch
StreamingMediaWorld
Web Developer's Journal
Web Developer's Virtual Library
WebDeveloper.com
Webreference
Web Hosts
XMLfiles.com

Be a Commerce Partner

IT
Developer
Internet News
Small Business
Personal Technology
International

Search internet.com
Advertise
Corporate Info
Newsletters
Tech Jobs
E-mail Offers

Introduction to DTD

by Jan Egil Refsnes

The purpose of a DTD is to define the legal building blocks of an XML document. It defines the document structure with a list of legal elements. A DTD can be declared inline in your XML document, or as an external reference.

Internal DTD

This is an XML document with a Document Type Definition: (Open it in IE5, and select view source)

<?xml version="1.0"?>
<!DOCTYPE note [
  <!ELEMENT note    (to,from,heading,body)>
  <!ELEMENT to      (#PCDATA)>
  <!ELEMENT from    (#PCDATA)>
  <!ELEMENT heading (#PCDATA)>
  <!ELEMENT body    (#PCDATA)>
]>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

The DTD is interpreted like this:
!ELEMENT note (in line 2) defines the element "note" as having four elements: "to,from,heading,body".
!ELEMENT to (in line 3) defines the "to" element to be of the type "CDATA".
!ELEMENT from (in line 4) defines the "from" element to be of the type "CDATA"
and so on.....

External DTD

This is the same XML document with an external DTD: (Open it in IE5, and select view source)

<?xml version="1.0"?>
<!DOCTYPE note SYSTEM "note.dtd">
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

This is a copy of the file "note.dtd" containing the Document Type Definition:

<?xml version="1.0"?>
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>

Why use a DTD?

XML provides an application independent way of sharing data. With a DTD, independent groups of people can agree to use a common DTD for interchanging data. Your application can use a standard DTD to verify that data that you receive from the outside world is valid. You can also use a DTD to verify your own data.

A lot of forums are emerging to define standard DTDs for almost everything in the areas of data exchange. Take a look at: CommerceNet's XML exchange and http://www.schema.net.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

DevX XML Content

- Create XML from an Array
- Utilizing a Multi-Core System with the Actor Model
- Why Migrate to the Semantic Web?
- PDC 2008 Delivers the Goods
- Creating Simple Firefox "Add-ons" with Ubiquity

Jump to : Top Of Page or HOME

Introduction to DTD

Internal DTD

External DTD

Why use a DTD?

Whitepapers and eBooks

Webcasts

Downloads and eKits

Tutorials and Demos