OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.


Help: OASIS Mailing Lists Help | MarkMail Help



   Re: DTDs vs Schemas

[ Lists Home | Date Index | Thread Index ]
  • From: Rick Jelliffe <ricko@allette.com.au>
  • To: xml-dev@lists.xml.org
  • Date: Thu, 28 Dec 2000 12:51:53 +0800

A DTD is a set of declarations and comments that allow you to state important invariants about a document, removing constants to a header.  This helps manageability (e.g., entity declarations and default attribute values), quality assurrance (e.g., element validity against a content model) and de-couples the creators of a document from the users of it to a certain extent. 
Unlike DTDs, W3C XML Schemas uses XML element syntax, are namespace-aware and provide the kinds of datatyping that people expect. They will be most helpful  for automatically generating optimized interfaces which accept or generate documents, for example SQL and Java systems.  W3C XML Schemas content models are mcuh more sophisticated than DTDs; they have many features to support extensibility, such as wildcarding and substitution groups.  W3C XML Schemas schemas will probably not be downloaded over the WWW at the same time as the document; they will tend to be built-in.
DTDs operate on the raw information of the document right after it is parsed--declaration recognition is built into all XML proessors (though only validating parsers make use of all the information in the declarations); W3C XML Schemas operate on the "information set" of the document as a separate stage (though how much the information set will be augmented by schema-processing a document is not being defined yet.)  A simple DTD may correspond to a more complex W3C XML Schema schema, and vice versa; a complicated DTD (with lots of parameter entities and INCLUDE./IGNORE sections) may be simpler in W3C XML Schemas.  A DTD can be transformed into a W3C XML Schemas schema and vice vera, but with some loss of information.
Rick Jelliffe
From: bigbadz

Hello all,

I am fairly new to XML and trying to understand the difference between DTDs and schemas. Is one a subset of the other? What are the key objectives to each? Can someone briefly  


News | XML in Industry | Calendar | XML Registry
Marketplace | Resources | MyXML.org | Sponsors | Privacy Statement

Copyright 2001 XML.org. This site is hosted by OASIS