XML and the Many Metamodels of Enterprise Metadata

Enterprise metadata appears in many languages and formats. XML provides a standard and consistent language for metadata, simplifying both interchange and parsing. But simply storing metadata as an XML file (be it XSD, BPEL, WSDL, J2EE EJB descriptors files, or any of dozens of proprietary formats) does not automatically and formally capture the full richness of the given metadata language. Even if XSDs are used to constrain syntax, they cannot define all possible structures and relationships, nor can they express the meaning of metadata in its business context.

Borenstein, Joram and Joshua Fox. IDEAlliance (2005). Articles>Information Design>Metadata>XML