An XML schema from the W3C. It is a superset of DTD, which is the standard SGML schema. Unlike DTD, W3C XML Schema is written in XML syntax, which although more verbose than DTD, can be created with any XML tools. Following is an example of W3C XML Schema statements that define first and last name, followed by tags in actual use within the document. The xsd prefix is defined elsewhere in the schema to refer to the XML namespace that is being used. For information, visit www.w3.org/XML/Schema. W3C XML Schema is informally known as "XSD." See XML schema, XML repository, DTD, XQuery and XML.