W3C XML Schema is a schema-definition language expressed in XML syntax. To avoid ambiguity, W3C XML Schema is often referred to as XSD Schema because in an earlier version it was called XML Schema Definition Language. Recently, the abbreviation WXS has also come into use to refer to the W3C XML Schema language.
Other schema languages are expressed in XML syntax, such as RELAX NG (a combination of TREX and RELAX) and XDR (XML Data Reduced, from Microsoft).
In this section, you are introduced to some of the reasons why W3C XML Schema was developed as an alternative schema mechanism to the Document Type Definition (DTD). ...