The W3C XML Schema Definition Language is a way of describing and constraining the content of XML documents.

The XML Schema specification consists of three parts. One part defines a set of simple datatypes, which can be associated with XML element types and attributes; this allows XML software to do a better job of managing dates, numbers, and other special forms of information. The second part of the specification proposes methods for describing the structure and constraining the contents of XML documents, and defines the rules governing schema validation of documents. The third part is a primer that explains what schemas are, how they differ from DTDs, and how one builds a schema.

XML Schema introduces new levels of flexibility that may accelerate the adoption of XML for significant industrial use. For example, a schema author can build a schema that borrows from a previous schema, but overrides it where new unique features are needed. XML Schema allows the author to determine which parts of a document may be validated, or identify parts of a document where a schema may apply. XML Schema also provides a way for users of e-commerce systems to choose which XML Schema they use to validate elements in a given namespace, thus providing better assurance in e-commerce transactions and greater security against unauthorized changes to validation rules. Further, as XML Schema are XML documents themselves, they may be managed by XML authoring tools, or through XSLT. The implementation of XML Schema in Virtuoso is based on the W3C XML Schema Specification .

For parsing the schema definitions the DTD definition of XML Schema is used. This definition was taken from XML Schema Part-1: Structures .