What is DTD?
DTD or Document Type Definition is used to define the structure and the legal elements and attributes of an XML document.
Why Use a DTD?
Independent groups of people can agree to use a standard DTD for interchanging data. An application can also verify that the XML data is valid.
An Internal DTD Declaration:
The DTD must be wrapped inside the <!DOCTYPE> definition, in case it is declared inside the XML file.
XML document with an internal DTD:
]>
Sapna
Tom
Meeting
Meeting on Monday Morning at 9 AM.
Explanation:
To view the DTD, we can select “view source”, in the XML file. Interpretation of the above DTD:
- !DOCTYPE note – Used to define that note is the root element of the document.
- !ELEMENT note – Used to define that the note element must contain the elements: “to, from, heading, body”.
- !ELEMENT to – Used to define that the “to” element is to be of type “#PCDATA”.
- !ELEMENT from – Used to define that the “from” element is to be of type “#PCDATA”.
- !ELEMENT heading – Used to define the heading element to be of type “#PCDATA”.
- !ELEMENT body – Used to define the body element to be of type “#PCDATA”
An External DTD Declaration:
A reference to the DTD file should be included in the <!DOCTYPE> definition, if the DTD is declared in an external file.
XML document with a reference to an external DTD:
Sapna
Tom
Meeting
Meeting on Monday Morning at 9 AM.
Note.dtd:
]>