XML DTD

• DTD stands for Document Type Definition, it is a markup language used to define the elements, attributes, and document structure of an XML document.
• A DTD document helps to validate the structure and content of an XML document to ensure that it meets certain rules and guidelines.

Syntax

The syntax for creating a DTD is as follows:

<!DOCTYPE root_element [
   <!-- DTD Declarations -->
]>

Example

<!DOCTYPE customers [
   <!ELEMENT customers (customer+)>
   <!ELEMENT customer (name, email, phone)>
   <!ELEMENT name (#PCDATA)>
   <!ELEMENT email (#PCDATA)>
   <!ELEMENT phone (#PCDATA)>
]>

Explanation

• <!DOCTYPE> - The Document Type Declaration starts the DTD section of the document.
• root_element - The name of the root element of the XML document.
• [] - The square brackets contain the declarations for the DTD.
• <!ELEMENT> - Defines a new element in the XML document.
• ( ) - Parentheses define the content model of an element.
• + - Indicates that there can be one or more occurrences of the element.
• #PCDATA - Defines the content of an element as text only.

Use

DTDs can be used to validate the structure and content of an XML document before it is processed by a web application, database or other system. It ensures that the XML document is valid and meets certain guidelines and standards.

Important Points

• DTDs are written in plain text and are generally easier to create and modify than other XML schema languages.
• DTDs are less powerful and expressive than other schema languages like XSD.
• DTDs can validate only the structure and content of an XML document, and not the data types of the elements and attributes.

Summary

DTD is a markup language used to define the structure of an XML document. It is used to validate the structure and content of an XML document before it is processed by a system. DTDs are written in plain text, and are generally easier to create and modify than other schema languages. However, they are less powerful than other schema languages like XSD.