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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<!-- $Id: package.html 570104 2007-08-27 13:28:24Z mrglavas $ -->
<html>
<body bgcolor="white">
<p>
This package provides an API for validation of XML documents. <em>Validation</em> is the process of verifying
that an XML document is an instance of a specified XML <em>schema</em>. An XML schema defines the
content model (also called a <em>grammar</em> or <em>vocabulary</em>) that its instance documents
will represent.
</p>
<p>
There are a number of popular technologies available for creating an XML schema. Some of the most
popular include:
<ul>
<li><strong>Document Type Definition (DTD)</strong> - XML's built-in schema language.</li>
<li><strong><a href="http://www.w3.org/XML/Schema">W3C XML Schema (WXS)</a></strong> - an object-oriented XML schema
language. WXS also provides a type system for constraining the character data of an XML document.
WXS is maintained by the <a href="http://www.w3.org">World Wide Web Consortium (W3C)</a> and is a W3C
Recommendation (that is, a ratified W3C standard specification).</li>
<li><strong><a href="http://www.relaxng.org">RELAX NG (RNG)</a></strong> - a pattern-based,
user-friendly XML schema language. RNG schemas may also use types to constrain XML character data.
RNG is maintained by the <a href="http://www.oasis-open.org">Organization for the Advancement of
Structured Information Standards (OASIS)</a> and is both an OASIS and an
<a href="http://www.iso.org">ISO (International Organization for Standardization)</a> standard.</li>
<li><strong><a href="http://www.schematron.com/">Schematron</a></strong> - a rules-based XML schema
language. Whereas DTD, WXS, and RNG are designed to express the structure of a content model,
Schematron is designed to enforce individual rules that are difficult or impossible to express
with other schema languages. Schematron is intended to supplement a schema written in
structural schema language such as the aforementioned. Schematron is in the process
of becoming an ISO standard.</li>
</ul>
</p>
<p>
Previous versions of JAXP supported validation as a feature of an XML parser, represented by
either a {@link javax.xml.parsers.SAXParser} or {@link javax.xml.parsers.DocumentBuilder} instance.
</p>
<p>
The JAXP validation API decouples the validation of an instance document from the parsing of an
XML document. This is advantageous for several reasons, some of which are:
<ul>
<li><strong>Support for additional schema languages.</strong> As of JDK 1.5, the two most
popular JAXP parser implementations, Crimson and Xerces, only support a subset of the available
XML schema languages. The Validation API provides a standard mechanism through which applications
may take of advantage of specialization validation libraries which support additional schema
languages.</li>
<li><strong>Easy runtime coupling of an XML instance and schema.</strong> Specifying the location
of a schema to use for validation with JAXP parsers can be confusing. The Validation API makes this
process simple (see <a href="#example-1">example</a> below).</li>
</ul>
</p>
<p>
<a name="example-1"><strong>Usage example</strong>.</a> The following example demonstrates validating
an XML document with the Validation API (for readability, some exception handling is not shown):
<pre>
// parse an XML document into a DOM tree
DocumentBuilderFactory parserFactory = DocumentBuilderFactory.newInstance();
parserFactory.setNamespaceAware(true);
DocumentBuilder parser = parserFactory.newDocumentBuilder();
Document document = parser.parse(new File("instance.xml"));
// create a SchemaFactory capable of understanding WXS schemas
SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
// load a WXS schema, represented by a Schema instance
Source schemaFile = new StreamSource(new File("mySchema.xsd"));
Schema schema = factory.newSchema(schemaFile);
// create a Validator instance, which can be used to validate an instance document
Validator validator = schema.newValidator();
// validate the DOM tree
try {
validator.validate(new DOMSource(document));
} catch (SAXException e) {
// instance document is invalid!
}
</pre>
</p>
<p>
The JAXP parsing API has been integrated with the Validation API. Applications may create a {@link javax.xml.validation.Schema} with the validation API
and associate it with a {@link javax.xml.parsers.DocumentBuilderFactory} or a {@link javax.xml.parsers.SAXParserFactory} instance
by using the {@link javax.xml.parsers.DocumentBuilderFactory#setSchema(Schema)} and {@link javax.xml.parsers.SAXParserFactory#setSchema(Schema)}
methods. <strong>You should not</strong> both set a schema and call <code>setValidating(true)</code> on a parser factory. The former technique
will cause parsers to use the new validation API; the latter will cause parsers to use their own internal validation
facilities. <strong>Turning on both of these options simultaneously will cause either redundant behavior or error conditions.</strong>
</p>
<p>
</body>
</html>
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