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Provides an API for validation of XML documents.  Validation is the
process of verifying that an XML document is an instance of a specified XML
schema.  An XML schema defines the content model (also called a
grammar or vocabulary) that its instance documents will
represent.


There are a number of popular technologies available for creating an XML schema.
Some of the most popular ones include:



 While JAXP supports validation as a feature of an XML parser, represented by either a SAXParser or DocumentBuilder instance, the Validation API is preferred. 

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:

    
    
  • Support for additional schema langauges.
        The JAXP parser implementations support only 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.
    
    • 
    
  • Easy runtime coupling of an XML instance and schema.
        Specifying the location of a schema to use for validation with JAXP
        parsers can be confusing. The Validation API makes this process simple
        (see example below).
    
    • 




Usage example. The following example
demonstrates validating an XML document with the Validation API
(for readability, some exception handling is not shown):

    // parse an XML document into a DOM tree
    DocumentBuilder parser = DocumentBuilderFactory.newInstance().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!
    }



 The JAXP parsing API has been integrated with the Validation API. Applications may create a Schema with the validation API and associate it with a DocumentBuilderFactory or a SAXParserFactory instance by using the DocumentBuilderFactory.setSchema(Schema) and SAXParserFactory.setSchema(Schema) methods. You should not both set a schema and call setValidating(true)
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. Turning on both of these options simultaneously will cause
either redundant behavior or error conditions.

Since:1.5
/**
 * <p>
 * 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>
 * There are a number of popular technologies available for creating an XML schema.
 * Some of the most popular ones 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://standards.iso.org/ittf/PubliclyAvailableStandards/c055982_ISO_IEC_19757-3_2016.zip">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 <a href="http://standards.iso.org/ittf/PubliclyAvailableStandards/index.html">an ISO standard</a>.
 *     </li>
 * </ul>
 * <p>
 * While JAXP supports validation as a feature of an XML parser, represented by
 * either a {@link javax.xml.parsers.SAXParser} or {@link javax.xml.parsers.DocumentBuilder}
 * instance, the {@code Validation} API is preferred.
 *
 * <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 langauges.</strong>
 *         The JAXP parser implementations support only 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>
 * <a id="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
 *     DocumentBuilder parser = DocumentBuilderFactory.newInstance().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>
 * 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>
 *
 *
 * @since 1.5
 */

package javax.xml.validation;