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<h1>Why Use XML Schemas?</h1>
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<p class="intro">XML Schemas are much more powerful than DTDs.</p>
<hr />
<h2>XML Schemas Support Data Types</h2>
<p>One of the greatest strength of XML Schemas is the support for data types.</p>
<p>With support for data types:</p>
<ul>
<li>It is easier to describe allowable document content</li>
<li>It is easier to validate the correctness of data</li>
<li>It is easier to work with data from a database</li>
<li>It is easier to define data facets (restrictions on data)</li>
<li>It is easier to define data patterns (data formats)</li>
<li>It is easier to convert data between different data types</li>
</ul>
<hr />
<h2>XML Schemas use XML Syntax</h2>
<p>Another great strength about XML Schemas is that they are written in XML.</p>
<p>Some benefits of that XML Schemas are written in XML:</p>
<ul>
<li>You don't have to learn a new language</li>
<li>You can use your XML editor to edit your Schema files</li>
<li>You can use your XML parser to parse your Schema files</li>
<li>You can manipulate your Schema with the XML DOM</li>
<li>You can transform your Schema with XSLT</li>
</ul>
<hr />
<h2>XML Schemas Secure Data Communication</h2>
<p>When sending data from a sender to a receiver, it is essential that both parts
have the same "expectations" about the content.</p>
<p>With XML Schemas, the sender can describe the data in a way that the receiver
will understand.</p>
<p>A date like: "03-11-2004" will, in some countries, be interpreted as 3.November
and in other countries as 11.March.</p>
<p>However, an XML element with a data type
like this:</p>
<p><date type="date">2004-03-11</date></p>
<p>ensures a mutual understanding of the content, because the XML data type "date"
requires the format "YYYY-MM-DD".</p>
<hr />
<h2>XML Schemas are Extensible</h2>
<p>XML Schemas are extensible, because they are written in XML.</p>
<p>With an extensible Schema definition you can:</p>
<ul>
<li>Reuse your Schema in other Schemas</li>
<li>Create your own data types derived from the standard types</li>
<li>Reference multiple schemas in the same document</li>
</ul>
<hr />
<h2>Well-Formed is not Enough</h2>
<p>A well-formed XML document is a document that conforms to the XML syntax
rules, like:</p>
<ul>
<li>it must begin with the XML declaration</li>
<li>it must have one unique root element</li>
<li>start-tags must have matching end-tags</li>
<li>elements are case sensitive</li>
<li>all elements must be closed</li>
<li>all elements must be properly nested</li>
<li>all attribute values must be quoted</li>
<li>entities must be used for special characters</li>
</ul>
<p>Even if documents are well-formed they can still contain errors, and those errors can have serious consequences.</p>
<p>Think of the following situation: you order 5 gross of laser printers, instead of 5 laser
printers. With XML Schemas, most of these errors can be caught by your
validating software.</p>
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