Lesson 6: Authoring XML Schemas

An XML Schema is an XML-based syntax for defining how an XML document is marked up. XML Schema is a schema specification recommended by Microsoft and it has many advantages over document type definition (DTD), the initial schema specification for defining an XML model. DTDs have many drawbacks, including the use of non-XML syntax, no support for datatyping, and non-extensibility. For example, DTDs do not allow you to define element content as anything other than another element or a string. For more information about DTDs, see the Worldwide Web Consortium (W3C) XML Recommendation. XML Schema improves upon DTDs in several ways, including the use of XML syntax, andsupport for datatyping and namespaces. For example, an XML Schema allows you to specify an element as an integer, a float, a Boolean, a URL, and so on.

http://msdn.microsoft.com/library/en-us/xmlsdk30/htm/xmtuttut6authoringschemas.asp?frame=true