1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> 2 <!-- $Id: package.html 570104 2007-08-27 13:28:24Z mrglavas $ --> 3 <html> 4 <body bgcolor="white"> 5 <p> 6 This package provides an API for validation of XML documents. <em>Validation</em> is the process of verifying 7 that an XML document is an instance of a specified XML <em>schema</em>. An XML schema defines the 8 content model (also called a <em>grammar</em> or <em>vocabulary</em>) that its instance documents 9 will represent. 10 </p> 11 <p> 12 There are a number of popular technologies available for creating an XML schema. Some of the most 13 popular include: 14 <ul> 15 <li><strong>Document Type Definition (DTD)</strong> - XML's built-in schema language.</li> 16 <li><strong><a href="http://www.w3.org/XML/Schema">W3C XML Schema (WXS)</a></strong> - an object-oriented XML schema 17 language. WXS also provides a type system for constraining the character data of an XML document. 18 WXS is maintained by the <a href="http://www.w3.org">World Wide Web Consortium (W3C)</a> and is a W3C 19 Recommendation (that is, a ratified W3C standard specification).</li> 20 <li><strong><a href="http://www.relaxng.org">RELAX NG (RNG)</a></strong> - a pattern-based, 21 user-friendly XML schema language. RNG schemas may also use types to constrain XML character data. 22 RNG is maintained by the <a href="http://www.oasis-open.org">Organization for the Advancement of 23 Structured Information Standards (OASIS)</a> and is both an OASIS and an 24 <a href="http://www.iso.org">ISO (International Organization for Standardization)</a> standard.</li> 25 <li><strong><a href="http://www.schematron.com/">Schematron</a></strong> - a rules-based XML schema 26 language. Whereas DTD, WXS, and RNG are designed to express the structure of a content model, 27 Schematron is designed to enforce individual rules that are difficult or impossible to express 28 with other schema languages. Schematron is intended to supplement a schema written in 29 structural schema language such as the aforementioned. Schematron is in the process 30 of becoming an ISO standard.</li> 31 </ul> 32 </p> 33 <p> 34 Previous versions of JAXP supported validation as a feature of an XML parser, represented by 35 either a {@link javax.xml.parsers.SAXParser} or {@link javax.xml.parsers.DocumentBuilder} instance. 36 </p> 37 <p> 38 The JAXP validation API decouples the validation of an instance document from the parsing of an 39 XML document. This is advantageous for several reasons, some of which are: 40 <ul> 41 <li><strong>Support for additional schema languages.</strong> As of JDK 1.5, the two most 42 popular JAXP parser implementations, Crimson and Xerces, only support a subset of the available 43 XML schema languages. The Validation API provides a standard mechanism through which applications 44 may take of advantage of specialization validation libraries which support additional schema 45 languages.</li> 46 <li><strong>Easy runtime coupling of an XML instance and schema.</strong> Specifying the location 47 of a schema to use for validation with JAXP parsers can be confusing. The Validation API makes this 48 process simple (see <a href="#example-1">example</a> below).</li> 49 </ul> 50 </p> 51 <p> 52 <a name="example-1"><strong>Usage example</strong>.</a> The following example demonstrates validating 53 an XML document with the Validation API (for readability, some exception handling is not shown): 54 <pre> 55 56 // parse an XML document into a DOM tree 57 DocumentBuilderFactory parserFactory = DocumentBuilderFactory.newInstance(); 58 parserFactory.setNamespaceAware(true); 59 DocumentBuilder parser = parserFactory.newDocumentBuilder(); 60 Document document = parser.parse(new File("instance.xml")); 61 62 // create a SchemaFactory capable of understanding WXS schemas 63 SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI); 64 65 // load a WXS schema, represented by a Schema instance 66 Source schemaFile = new StreamSource(new File("mySchema.xsd")); 67 Schema schema = factory.newSchema(schemaFile); 68 69 // create a Validator instance, which can be used to validate an instance document 70 Validator validator = schema.newValidator(); 71 72 // validate the DOM tree 73 try { 74 validator.validate(new DOMSource(document)); 75 } catch (SAXException e) { 76 // instance document is invalid! 77 } 78 </pre> 79 </p> 80 <p> 81 The JAXP parsing API has been integrated with the Validation API. Applications may create a {@link javax.xml.validation.Schema} with the validation API 82 and associate it with a {@link javax.xml.parsers.DocumentBuilderFactory} or a {@link javax.xml.parsers.SAXParserFactory} instance 83 by using the {@link javax.xml.parsers.DocumentBuilderFactory#setSchema(Schema)} and {@link javax.xml.parsers.SAXParserFactory#setSchema(Schema)} 84 methods. <strong>You should not</strong> both set a schema and call <code>setValidating(true)</code> on a parser factory. The former technique 85 will cause parsers to use the new validation API; the latter will cause parsers to use their own internal validation 86 facilities. <strong>Turning on both of these options simultaneously will cause either redundant behavior or error conditions.</strong> 87 </p> 88 <p> 89 90 </body> 91 </html> 92
