What are XML schemas? How are they different from DTDs?
While XML 1.0 supplies a mechanismthe DTDfor defining the content model of an XML document, it is evident that a more comprehensive and rigorous method of defining a content model is needed. An XML schema is the definition (both in terms of its organization and its data types) of a specific XML structure. An XML schema uses the XML Schema language to specify how each type of element in the schema is defined and what data type that element has associated with it. Perhaps one of the most compelling features of schemas compared to DTDs is that a schema is itself an XML document. This means that it can be read by the same tools that read the XML it describes. Microsoft’s XML services currently support XML-Data schemas, representing a snapshot of the W3C Schema activity at the time Internet Explorer 5 shipped in March 1999. XML-Data schemas allow developers to add data types to their XML documents and define open content models. Such extensions to the functionality of DTDs are critical to p
