.NET & XML

Using W3C XML Schema

An XML Schema document (XSD), like an XSLT stylesheet, is itself an XML document. It may contain an XML declaration, and must contain a namespace declaration for the URI http://www.w3.org/2001/XMLSchema. This namespace is traditionally mapped to the prefix xs. The document element of an XSD is xs:schema; the simplest possible XSD, therefore, is the following:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" />

Of course, this XSD defines no structure, so it is mostly useless. To be more useful, it should include at least one element, representing the document element of the XML document it describes:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="Customer" />
</xs:schema>

The xs:element element is called a particle. A particle can be thought of as representing a single unit of markup, or a grouping of such units. Other particles include xs:attribute, xs:choice, and xs:sequence, among others. xs:all, xs:sequence and xs:choice are also compositors, elements that define groups of particles.

A document using this schema would need to have the following content in order to be valid:

<Customer />

Tip

You may have already noticed that I’ve deviated from the style used in earlier parts of this book by capitalizing the first letter of the Customer element. I’ll be capitalizing the first letter of every element and attribute name in this XSD. Hold that thought! I’ll explain the different ...