XML Document Type Definition

Introduction to XML DTD

DTD stands for Document Type Definition.
It is used to validate the XML documents.
XML provides facility to create your own DTDs for XML document.
DTD specifies the structure of the XML document.
DTD is part of the file or separate document file.

Types of DTD

There are two types of DTDs:
a) Internal DTD.
b) External DTD.

Internal DTD vs External DTD.

Internal DTD	External DTD
Internal DTD is part of the document.	External DTD is a separate file.
The scope is limited to the document which is created.	It is accessible across the multiple documents.
Syntax: <!DOCTYPE rootelement[element and attribute declarations]>	Syntax: <!DOCTYPE rootelement\|SYSTEM “path of .dtd file”>

Components of DTD

We have to associate the .xml file with the DTD and run the same .xml file in the browser.

Syntax for declaring elements in DTD:
<!ELEMENT elementname (content-type or content-model)>

Where elementname specifies the name of the element present in the xml document and content-type or content-model specifies whether the element contains textual data or other elements.

The three types of elements are as follows:

Element type	Description	DTD Declaration
Empty	Contains attributes, but can't contain text or any other element.	<!Element elementname EMPTY>
Unrestricted	Contains text content or any other element.	<!ELEMENT elementname ANY>
Container	Contain another elements.	<!ELEMENT elementname (elementname, elementname [elementname])>

Declaring Attributes in DTD

Syntax:
<!!ATTLIST elementname atributename valuetype [atributetype] [“default”]>

Each attribute declaration must include at least the attribute name in a DTD as follows:

Value Type	Description
PCDATA	Represents the plain text values.
ID	Assigns unique value to each element in the document.
(enumerated)	Assigns a specific range of values which is specified within parenthesis.

Example : Declaring Attributes in DTD

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
     <!DOCTYPE Employee
[
     <!ELEMENT address (name,company,phone)>
     <!ELEMENT name (#PCDATA)>
     <!ELEMENT company (#PCDATA)>
     <!ELEMENT phone (#PCDATA)>
]>
<address>
     <name>Mayuri S</name>
     <company>TutorialRide</company>
     <phone>91-9800000000</phone>
</address>