标签：des style blog http color io ar strong for
A Document Type Definition (DTD) defines 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.
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" encoding="UTF-8"?> <!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 (select "view source" or "view page source" to view the DTD)
The DTD above is interpreted like this:
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" encoding="UTF-8"?> <!DOCTYPE note SYSTEM "C:\Users\maijunjin\Desktop\dtd\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:
<?xml version="1.0" encoding="UTF-8"?> <!ELEMENT note (to,from,heading,body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)>
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.
标签：des style blog http color io ar strong for
原文地址：http://www.cnblogs.com/ghgyj/p/3991904.html
