XML Data Types Reference
The World Wide Web Consortium (W3C) XML Schema Part 2: DataTypes is the specification for defining data types used in XML Schemas. This specification defines built-in primitive data types, derived data types, and facets.
The following diagram shows the type hierarchy.
See Also
XML Schema Reference (XSD) | Primitive XML Data Types | Derived XML Data Types | Data Type Facets
Other Resources 
World Wide Web Consortium (W3C) XML Schema Part 2: Datatypes