View source for DTD

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== Definiton ==

'''Document Type Definition (DTD)''' is an SGML and [[XML]] schema language. A DTD is used to define and describe the elements and groups thereof and the order in which they are allowed (or not) to appear within an SGML or XML document. A document must conform to the specifications of an associated DTD (i.e. be ''valid'') before it can be processed for output.

See also: [[DTD tutorial]]

== Structure ==
DTDs are made up of element and attribute-list declarations. 
*'''elements''' declare what types of data, how and whether or not they are allowed within other declared elements.
*'''attribute-lists''' declare the attributes allowed for each element and their value type.

For example, the following XML document would be valid according to the DTD that follows.
<code>
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE people_list SYSTEM "example.dtd">
 <people>
   <person gender="female">
      <name>
         <first>Jane</first>
         <middle>Jean</middle>
         <last>Doe</last>
         <maidenName></maidenName>
      </name>
   </person>
 <people>
</code>

Corresponding DTD:
<code> 
 <!ELEMENT people (person*)> //* one or more person must appear in the list
 <!ELEMENT person (name)> // person element must have exactly one name element
  <!ATTLIST person  gender CDATA #REQUIRED> //the person element must have an attribute gender
 <!ELEMENT name (first, middle?, last, maidenName?)> //middle and maidenName elements are optional
 <!ELEMENT first (#PCDATA)>
 <!ELEMENT middle (#PCDATA)>
 <!ELEMENT last (#PCDATA)>
 <!ELEMENT maidenName (#PCDATA)>
</code>

None of the above documents define the style of the documents. They describe the content and its syntactical expression (descriptive language), not its form or style (unlike [[Wikipedia:HTML | HTML]] or [[XHTML]] that provide built-in basic formatting). The style and form of the document is attributed during processing (e.g. through [[Wikipedia:Cascading Style Sheets | CSS]], [[Wikipedia:XSLT | XSLT]], )

Interpretive software can used to convert the "structured" document for multiple output formats including print and web pages containing HTML (hypertext markup language) or directly [[XML]] (extensible markup language).

See the [[DTD tutorial]] for details.

== Alternatives ==

* [[XML Schema]] - a W3C standard
* [[Relax NG]] - an easier more XML-intuitive schema language

== Use of DTDs in education ==

DTDs and other schema languages lend themselves to particular learning activities and pedagogical scenarios where either [[knowledge representation]]s and requirements, the creation of [[Ontology | ontologies]] or the definition of rubrics are individually or collaboratively constructed.

;Examples:
The English Department at the University of Georgia has composition students collaboratively create their own DTDs from templates, that describe the components and evaluation criteria for various writing [[Writing-to-learn#Genre debate | genres]] and  such as narrative, expository or argumentative writing.

[[Educational modelling language]]s rather tend to be specified with Relax NG or XML Schema ...

{{comment| others needed}}[[User:Kalli|KBenetos]]

==References==
* [http://en.wikipedia.org/wiki/Document_Type_Definition Wikipedia: Document Type Definition]
* Paille, G. Open School (A Division of the Open Learning Agency)British Columbia, Canada [http://netcamp.prn.bc.ca/sgml/naweb2.html]

[[Category: XML]]
[[Category: Standards]]