What is an XML Schema Definition file?

An XML Schema Definition (XSD) file provides the syntax and defines a way in which elements and attributes can be represented in a XML document.

It also advocates that the given XML document should be of a specific format and specific data type. XSD is fully recommended by W3C consortium as a standard for defining an XML document, and has replaced the use of Document Type Definition (DTD) files. For more information on XSD, please refer to the W3C consortium web site at http://www.w3.org.