XML Schema

XML Schema, published as a W3C Recommendation in May 2001, is an XML schema language. It was the first separate schema language for XML to achieve Recommendation status by the W3C.

Since other XML schema languages such as RELAX NG now exist, it is important to cite this language as either XML Schema or W3C XML Schema, always with the word Schema capitalized. It is also often referenced with the acronym WXS. An XML Schema instance may be referenced as an XSD (XML Schema Definition), and typically has the filename extension ".xsd".

In its appendix of references, XML Schema acknowledges the influence of DTD and other early XML schema efforts such as DDML, SOX, XML-Data, and Microsoft and Commerce One, respectively, have both announced that they would support XML Schema for their new developments, so W3C XML Schema should become the only surviving member of this family.

After XML Schema-based validation, it is possible to express a document's structure and content in terms of the data model that was implicit during validation. This collection of information is called the Post-Schema Validation Infoset (PSVI).