THE XML REVOLUTION - TECHNOLOGIES FOR THE FUTURE WEB

XML Schema

W3C Recommendation, May 2001.

Consists of two parts:

Main features:

XML syntax (there is a Schema for Schemas)
uses and supports Namespaces
object-oriented-like type system for declarations (with inheritance, subsumption, abstract types, and finals)
global (=top-level) and local (=inlined) type definitions
modularization (schema inclusion and redefinitions)
structured self-documentation
cardinality constraints for sub-elements
nil values (missing content)
attribute and element defaults
any-element, any-attribute
uniqueness constraints and ID/IDREF attribute scope
regular expressions for specifying valid chardata and attribute values
lots of built-in data types for chardata and attribute values

Yes, it is big and complicated! (Part 1 of the spec alone is more than 150 dense pages...)