| Author: Shivshanker Cheral 14 Jul 2008 | Member Level: Diamond | Rating:  Points: 0 |
The purpose of a DTD (Document Type Definition) is to define the legal building blocks of an XML document. It defines the document structure with a list of legal elements and attributes.
A DTD can be declared inline inside an XML document, or as an external reference.
--------------------------------------------------------------------------------
Internal DTD Declaration
If the DTD is declared inside the XML file, it should be wrapped in a DOCTYPE definition with the following syntax:
<!DOCTYPE root-element [element-declarations]>
Example XML document with an internal DTD:
<?xml version="1.0"?>
<!DOCTYPE note [
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
]>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend</body>
</note>
Open the XML file above in your browser, and select view source or view page source to view the DTD.
The DTD above is interpreted like this:
!DOCTYPE note defines that the root element of this document is note.
!ELEMENT note defines that the note element contains four elements: "to,from,heading,body".
!ELEMENT to defines the to element to be of the type "#PCDATA".
!ELEMENT from defines the from element to be of the type "#PCDATA".
!ELEMENT heading defines the heading element to be of the type "#PCDATA".
!ELEMENT body defines the body element to be of the type "#PCDATA".
--------------------------------------------------------------------------------
External DTD Declaration
If the DTD is declared in an external file, it should be wrapped in a DOCTYPE definition with the following syntax:
<!DOCTYPE root-element SYSTEM "filename">
This is the same XML document as above, but with an external DTD (Open it, and select view source):
<?xml version="1.0"?>
<!DOCTYPE note SYSTEM "note.dtd">
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
And this is the file "note.dtd" which contains the DTD:
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
--------------------------------------------------------------------------------
Why Use a DTD?
With a DTD, each of your XML files can carry a description of its own format.
With a DTD, independent groups of people can agree to use a standard DTD for interchanging data.
Your application can use a standard DTD to verify that the data you receive from the outside world is valid.
You can also use a DTD to verify your own data.
for more
http://www.xmlfiles.com/dtd/dtd_intro.asp
http://www.w3schools.com/DTD/dtd_intro.asp
|
| Author: vasantha 17 Jul 2008 | Member Level: Bronze | Rating: Points: 4 |
With a DTD, each of your XML files can carry a description of its own format.
With a DTD, independent groups of people can agree to use a standard DTD for interchanging data.
Your application can use a standard DTD to verify that the data you receive from the outside world is valid.
You can also use a DTD to verify your own data.
|