====== Introduction to XML Schema ====== XML Schema is an XML-based alternative to DTD. An XML schema describes the structure of an XML document. The XML Schema language is also referred to as XML Schema Definition (XSD). ===== What You Should Already Know ===== Before you continue you should have a basic understanding of the following: * HTML / XHTML * XML and XML Namespaces * A basic understanding of DTD If you want to study these subjects first, find the tutorials on our [[http://www.w3schools.com/default.asp|Home page]]. ===== What is an XML Schema? ===== The purpose of an XML Schema is to define the legal building blocks of an XML document, just like a DTD. An XML Schema: * defines elements that can appear in a document * defines attributes that can appear in a document * defines which elements are child elements * defines the order of child elements * defines the number of child elements * defines whether an element is empty or can include text * defines data types for elements and attributes * defines default and fixed values for elements and attributes ===== XML Schemas are the Successors of DTDs ===== We think that very soon XML Schemas will be used in most Web applications as a replacement for DTDs. Here are some reasons: * XML Schemas are extensible to future additions * XML Schemas are richer and more powerful than DTDs * XML Schemas are written in XML * XML Schemas support data types * XML Schemas support namespaces ===== XML Schema is a W3C Recommendation ===== XML Schema became a W3C Recommendation 02. May 2001. You can read more about the XML Schema standard in our [[http://www.w3schools.com/w3c/w3c_schema.asp|W3C tutorial]].