Introduction to XML Document Type Definition by Examples

Posted by Imed Bouchrika on November 27, 2013 in XML No Comments

The purpose of a DTD (Document Type Definition) is to define a set of rules describing the structure of an XML document with a list of legal elements and attributes.

The general structure of a DTD as as follows :

[info]The ROOT_ELEMENT is the root element of the XML document[/info]

For the DTD, the three main building blocks are as follows:

  1. <!ELEMENT ….
  2. <!ATTLIST ….
  3. <!ENTITY ….

[info]Click here to Practice and Learn Document Type Definition to validate XML online[/info]

For the sake of simplicity, DTD syntax is illustrated using examples in the following table:

DTD Explanation and Examples
<!ELEMENT element-name EMPTY>
Example : <!ELEMENT br EMPTY> 		Empty elements are declared with the category keyword EMPTY:
<br />
<!ELEMENT element-name (#PCDATA)>
Example : <!ELEMENT title (#PCDATA)> 		Elements with only parsed character data are declared with #PCDATA inside parentheses:
<title>Java Programming</title>
<!ELEMENT element-name (child1,child2)>




]
>
Elements with one or more children are declared with the name of the children elements inside parentheses


   Feature Extraction
   Mark Nixon
<!ELEMENT element-name (child-name+)>
Example : <!ELEMENT Student (country+)> 		The + sign in the example above declares that the child element “country” must occur ONE or More times inside the “Student” element.
<!ELEMENT element-name (child-name?)>
Example : <!ELEMENT Student (Tutor?)> 		The ? sign in the example above declares that the child element “Tutor” must occur ZERO or ONE times inside the “Student” element.
<!ELEMENT element-name (child-name*)>
Example : <!ELEMENT Student (module*)> 		The * sign in the example above declares that the child element “module” must occur ZERO or More times inside the “Student” element.
<!ELEMENT element-name (option1|option2)>
Example : <!ELEMENT Student (Tutor|Supervisor)> 		The example declares that the “Student” element must contain either a “Tutor” or a “Supervisor” element.
<!ELEMENT element-name (option1|option2)>
Example : <!ELEMENT Student (Tutor|Supervisor)> 		The example declares that the “Student” element must contain either a “Tutor” or a “Supervisor” element.
<!ATTLIST element-name attr-name attr-type attr-value>
Example : <!ATTLIST book language CDATA “english”> 		The element book has an attribute named language of type CDATA with a default value “english”
The possible values for the attr-values are listed as:
Example : <!ATTLIST country code CDATA #REQUIRED> The element country has an attribute named code of type CDATA with a required value
Example : <!ATTLIST city mayor CDATA #IMPLIED> The element city has an attribute named mayor of type CDATA but is not required.
Example : <!ATTLIST car wheels CDATA #FIXED “4”> The element car has an attribute named wheels of type CDATA with a fixed value of “4”
Example : <!ATTLIST Bus color (white|blue|green) “white”> The element Bushas an attribute named color that is within the set of choices (white OR blue OR green). The default value is white

Example : <!ENTITY copyright “Copyright by Imed Bouchrika”> 		Entities are variables used to define shortcuts to standard text or special characters.
Example <website>&copyright<website>

DTD document can be integrated within the XML document as shown in the example below:







]>

Hou
Asma

[info]We use the statement standalone=”yes” within the XML header[/info]

Or instead, the DTD can created on a separate file, for example mydata.dtd and called as shown below from the XML document




Hou
Asma

Questions

1 CDATA is a character data for attributes? is there any other data types ?

2 We can store data either within an element or attribue, which one is better to use ?

About Author

by Imed Bouchrika

Dr. Imed Bouchrika received his PhD degrees in Electronics and Computer Science from the University of Southampton in United Kingdom in 2008. He has been in the industry as a software developer for over a decade primarily designing and developing interactive web applications. At the same time, he worked as a research fellow at the Image Processing research group at the University of Southampton investigating the potential use of gait as new biometric for forensic and security applications.

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