A Document Type Definition specifies the tags and
associated attributes that are permitted in an associated XML or
SGML document. In XML, the Document Type Definition is part of
the document prolog. The Document Type Definition may reside within the
XML document. Alternatively, the Document Type Definition may lie in a
separate file that is identified using a URI.
In recent times,
document designers have started to move away from the use
of Document Type Definition, using XML schema instead. XML schema are
seen as providing a more flexible means for specifying the
grammar of a class of XML documents.
Other topics in our resources on XML related to Document Type Definition include: