DocumentTypeDefinition was introduced in the XML standard as the schema language for XML. Because of the limited power of DTD and because it cannot handle XMLNamespaces in an acceptable way a lot of alternative schema languages have been developed.

• XMLSchema
• RelaxNG
• DocumentStructureDescription^? (DSD).

The schema languages that are currently used have been compared using a formal framework in TaxonomyOfXMLSchemaLanguagesUsingFormalLanguageTheory.

-- MartinBravenboer - 30 May 2002