XML Schema Definition

An XML Schema Definition (XSD) is an instance of an XML schema written in the W3C s XML Schema language. An XSD defines a type of XML document in terms of constraints upon what elements and attributes may appear, their relationship to each other, what types of data may be in them, and other things. It can be used with validation software in order to ascertain whether a particular XML document is of that type, and to produce a PSVI.

XSDs were the first World Wide Web Consortium-recommended XML schemas to provide a namespace- and datatype-aware alternative to using XML s built-in Document Type Definitions (DTDs).

XML Schema Definition files usually have the filename extension .xsd . A unique Internet Media Type is not yet registered for XSDs, so application/xml or text/xml should be used, as per RFC 3023.