WHAT YOU WILL LEARN IN THIS CHAPTER:
Like DTDs, XML Schemas are used for defining XML vocabularies. They describe the structure and content of XML documents in more detail than DTDs, and hence allow more precise validation.
Today, XML Schemas are a mature technology used in a variety of XML applications. Apart from their use in validation, aspects of XML Schemas are used in various other XML technologies such as XQuery and SOAP, which are covered in later chapters.
The XML Schema 1.0 specifications were first published by the W3C in 2001 and then revised to a Second Edition in 2004. The 2004 documents are currently the primary reference for XML Schema, although a 1.1 version is under development. At the time of this writing, these documents are at Candidate Recommendation status. The main ideas of the 1.1 specification are the same as the 1.0 version and this newer version is clearer and a little easier to read, so generally speaking it makes a better reference (a handful of changes and additions are covered at the end of this chapter). All the relevant specifications are available at www.w3.org/XML/Schema.