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<h1>Introduction to XML Schema</h1>
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<p class="intro">XML Schema is an XML-based alternative to DTD.</p>
<p class="intro">An XML schema describes the structure of an XML document.</p>
<p class="intro">The XML Schema language is also referred to as XML Schema
Definition (XSD).</p>
<hr />
<h2>What You Should Already Know</h2>
<p>Before you continue you should have a basic understanding of the following:</p>
<ul>
<li>HTML / XHTML</li>
<li>XML and XML Namespaces</li>
<li>A basic understanding of DTD</li>
</ul>
<p>If you want to study these subjects first, find the tutorials on our
<a href="../default.asp">Home page</a>.</p>
<hr />
<h2>What is an XML Schema?</h2>
<p>The purpose of an XML Schema is to define the legal building blocks of an XML
document, just like a DTD.</p>
<p>An XML Schema:</p>
<ul>
<li>defines elements that can appear in a document</li>
<li>defines attributes that can appear in a document</li>
<li>defines which elements are child elements</li>
<li>defines the order of child elements</li>
<li>defines the number of child elements</li>
<li>defines whether an element is empty or can include text</li>
<li>defines data types for elements and attributes</li>
<li>defines default and fixed values for elements and attributes</li>
</ul>
<hr />
<h2>XML Schemas are the Successors of DTDs</h2>
<p>We think that very soon XML Schemas will be used in most Web applications as a
replacement for DTDs. Here are some reasons:</p>
<ul>
<li>XML Schemas are extensible to future additions</li>
<li>XML Schemas are richer and more powerful than DTDs</li>
<li>XML Schemas are written in XML</li>
<li>XML Schemas support data types</li>
<li>XML Schemas support namespaces</li>
</ul>
<hr />
<h2>XML Schema is a W3C Standard</h2>
<p>XML Schema became a W3C Recommendation 02. May 2001.</p>
<p>You can read more about the XML Schema standard in our <a href="../w3c/default.asp">W3C tutorial</a>.</p>
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