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<!DOCTYPE faqs SYSTEM 'dtd/faqs.dtd'>
<faqs title='Using XML Schemas'>

  <faq title="Usage">
    <q>How do I validate against XML schema?</q>
    <a>
      <p>XML Schema 1.0 validation has been integrated with the 
	regular SAXParser and DOMParser classes, and also with the JAXP
      validation API using the XSD 1.0 Schema factory. No special classes are 
	required to parse documents that use a schema.</p>
      <p>For XML Schema 1.1 validation, the preferred way is to use the JAXP
      validation API, using the XSD 1.1 Schema factory. Here's an example: </p>
      <source>import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;

...

StreamSource[] schemaDocuments = /* created by your application */;
Source instanceDocument = /* created by your application */;

SchemaFactory sf = SchemaFactory.newInstance(
    "http://www.w3.org/XML/XMLSchema/v1.1");
Schema s = sf.newSchema(schemaDocuments);
Validator v = s.newValidator();
v.validate(instanceDocument);
</source>
      <p>Similar to XML Schema 1.0 validation using SAXParser and DOMParser classes that was
         available earlier with Xerces, the same has been enhanced to support XML Schema 1.1
         validation as well. To be able to do this, we need to construct the XSD 1.1 Schema factory
         with the following java statement, SchemaFactory.newInstance("http://www.w3.org/XML/XMLSchema/v1.1")
         and do the subsequent validation. 
      </p>
      <p>You can also refer to the JAXP sample, SourceValidator, where you
         can validate XML documents against 1.1 schemas by specifying an option "-xsd11"
         when running the sample.</p>
      <p>Each document that uses XML Schema grammars must specify the location of the
	grammars it uses by using an xsi:schemaLocation attribute if they use
	namespaces, and an xsi:noNamespaceSchemaLocation attribute
	otherwise.  These are usually placed on the root / top-level element 
	in the document, though they may occur on any element; for more details see <jump href="https://www.w3.org/TR/xmlschema-1/#composition-instances">XML Schema Part 1 section 4.3.2</jump>. 
	Here is an example with no target namespace: </p>
      <source>&lt;document
    xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
    xsi:noNamespaceSchemaLocation='document.xsd'&gt;
    ...
&lt;/document&gt;</source>
      <p>Here is an example with a target namespace. Note that it is an
	error to specify a different namespace than the target namespace
	defined in the Schema.</p>
      <source>&lt;document
    xmlns='http://my.com'
    xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' 
    xsi:schemaLocation='http://my.com document.xsd'&gt;
    ...
&lt;/document&gt;</source>
      <p>Review the sample file, 'data/personal.xsd' for an example of an XML 
	Schema grammar.</p>
      
    </a>
  </faq>
  <faq title="Using Entities and CDATA Sections">
    <q>How does the XML Schema processor treat entities and CDATA sections?</q>
    <a> 
      <p>According to the XML Infoset the infoset items contributing to the 
	<jump href='http://www.w3.org/TR/xml-infoset/#infoitem.character'>[character
	  information item]</jump> are: characters in the document, whether literally, as
	a character reference, or within a CDATA section, or within Entity
	Reference. The XML Schema specification 
	"requires as a precondition for assessment
	an information set as defined in [XML-Infoset]" 
	<jump href='http://www.w3.org/TR/xmlschema-1/#infoset'>(Appendix D)</jump> and thus Xerces might attempt to normalize data in an entity
	reference or CDATA section.  To preserve character data within entity references and 
	CDATA sections, 
	turn off http://apache.org/xml/features/validation/schema/normalized-value feature.
      </p>
    </a>
  </faq>
  <faq title="XPath 2.0 support for XML Schema 1.1 validation">
  	<q>How an XPath 2.0 engine is used for XML Schema 1.1 assertions and CTAs?</q>
  	<a>
  	   <p>XML Schema 1.1 assertions and CTAs require an XPath processor during evaluation. For XSD 1.1 assertions,
  	   full <jump href="http://www.w3.org/TR/xpath20/">XPath 2.0</jump> support is required. For XSD 1.1 CTAs the XSD schema engines can
  	   provide full XPath 2.0 support, or they can implement a <jump href="http://www.w3.org/TR/xmlschema11-1/#coss-ta">smaller XPath subset</jump>
  	   as defined by the XSD 1.1 language. For CTAs Xerces uses the XSD 1.1 CTA XPath subset language by default, but can be made to use the full XPath 2.0 support by
  	   setting the value of Xerces feature <code>http://apache.org/xml/features/validation/cta-full-xpath-checking</code> to 'true'.
  	   The native CTA XPath processor in Xerces-J was written for efficiency, so you will likely get better performance if your
  	   XPath expressions fall within the minimum subset defined by the XML Schema 1.1 specification. For full XPath 2.0 evaluation
  	   (for XSD 1.1 assertions, and optionally for CTAs), Xerces-J uses the <jump href="http://wiki.eclipse.org/PsychoPathXPathProcessor">Eclipse/PsychoPath XPath 2.0 engine</jump>.
  	   Xerces-J does bundle along a PsychoPath XPath 2.0 jar (which requires JDK 1.4 or later).
  	   </p>
  	   <p>
  	      We would like to acknowledge, work of following people for the XPath 2.0 support that comes with Xerces's
  	      XML Schema 1.1 processor: Andrea Bittau (responsible for the original design and implementation, of XPath 2.0
  	      processor that's been used by Xerces. Andrea donated his XPath 2.0 processor to the Eclipse Foundation, that
  	      Xerces uses.), Dave Carver (Dave helped to set up software infrastructure at Eclipse Foundation's Web Tools Platform project,
  	      for testing the XPath 2.0 processor as per W3C XPath 2.0 test suite. He also helped to improve compliance of
  	      XPath 2.0 processor, to the W3C XPath 2.0 test suite by providing numerous bug fixes and implementation.),
  	      Jesper Steen Moeller (Jesper as an Eclipse's Web Tools Platform committer, helped to improve the implementation
  	      of the XPath 2.0 processor).
  	   </p>
  	</a>
  </faq>
  <faq title="User defined error messages, for XML Schema 1.1 assertion failures">
     <q>How to specify a user defined error message, when an XML Schema 1.1 assertion returns a 'false' result?</q>
     <a>
        <p>When evaluation of an XSD 1.1 assertion fails the Xerces XML Schema validator would produce a default error message,
        which would say that which element or attribute was not validated successfully by an assertion and the schema type involved 
        during validation. It is however possible to, specify an user-defined error message for assertion failures. This is done by 
        specifying an attribute <code>"message"</code> in the XML namespace <code>'http://xerces.apache.org'</code> on an 
        <code>xs:assert</code> or <code>xs:assertion</code> element in the schema. In this case, the value of attribute <code>"message"</code> 
        is a text of user-defined assertion error message which is generated by the Xerces XML Schema validator when an assertion fails.
        </p>
        <p>
        While using <code>xs:assertion</code> facet within simple types, if a user defined error message is used, a user may
        dynamically construct the assertion error message by getting the value of XPath 2.0 context variable 
        <code>$value</code> into the error message. Following is an example of such an assertion error message:
        <code>xerces:message="The number {$value} is not divisible by 2"</code>. With such a description of assertion error message, 
        a value from XML instance document is assigned to a variable reference <code>{$value}</code> which is a defined keyword.
        During a validation failure, an error message for this example would be produced as follows,
        <code>"The number 3 is not divisible by 2"</code> (the variable reference <code>{$value}</code> is assigned a value 3).     
        </p>
        <note>
           User-defined error messages for assertion failures are not a standard feature of the XML Schema 1.1 specification, and 
           are a Xerces extension to help XML Schema document authors to specify a problem domain specific error messages.
        </note>
     </a>
  </faq>
  <faq title="XML Schema API">
    <q>Does Xerces provide access to the post schema validation infoset (PSVI)?</q>
    <a>
      <p>
	Xerces implements the <jump href="http://www.w3.org/Submission/2004/SUBM-xmlschema-api-20040309/">XML Schema API</jump> specification that defines an API for accessing and querying the post schema validation infoset (PSVI) as defined in <jump href='http://www.w3.org/TR/xmlschema-1/#PSVI_contributions'>
	  Contributions to the post-schema-validation infoset (Appendix C.2)</jump>. 
          This API also defines interfaces for loading XML schema documents. 
      </p>
      <p>For more information please refer to the 
         <link idref='api' anchor='xml-schema-api-documentation'>interfaces</link>.
      </p>
<note>The Xerces 2.6.2 release fixes a documentation bug in the <jump href="http://www.w3.org/Submission/2004/SUBM-xmlschema-api-20040309/">XML Schema API</jump>. In particular in the XSModel interface the order of the parameters in getTypeDefinition, getNotationDeclaration, getModelGroupDefinition, getElementDeclaration, getAttributeDeclaration, getAttributeGroup methods have been changed from (String namespace, String name) to (String name, String namespace). 
</note>
    </a>
  </faq>
  
  <faq title="Changes to PSVI">
    <q>What happened to the PSVI interfaces in org.apache.xerces.xni.psvi?</q>
    <a>
      <p>
        The PSVI interfaces which used to be part of the <code>org.apache.xerces.xni.psvi</code>
        and <code>org.apache.xerces.impl.xs.psvi</code> packages were modified and have been moved
        into the <jump href="http://www.w3.org/Submission/2004/SUBM-xmlschema-api-20040309/">XML Schema API</jump>.
      </p>
    </a>
  </faq>

  <faq title="Accessing PSVI via XNI">
    <q>How do I access PSVI via XNI?</q>
    <a> <p>From within an <code>XMLDocumentHandler</code>, one can retrieve PSVI
	information while in the scope of the document handler start/end element calls:</p>
      <source>import org.apache.xerces.xs.*;

...

public void startElement(QName element, XMLAttributes attributes,
    Augmentations augs) {
    ElementPSVI elemPSVI = (ElementPSVI)augs.getItem("ELEMENT_PSVI");
    // get PSVI items of this element out of elemPSVI
    short attemp = elemPSVI.getValidationAttempted();
    short validity = elemPSVI.getValidity();
    ...
}</source>
      <note>For more information, please refer to the API documentation
	for the XML Schema API.</note>
      
      <p>The above code shows how to retrieve PSVI information after
	elements/attributes are assessed. The other kind of information PSVI
	offers is the property
	<jump href="http://www.w3.org/TR/xmlschema-1/#e-schema_information">[schema information]</jump>.
	This property exposes all schema components in the schema that are used for
	assessment. These components and the schema itself are represented by
	interfaces in the <code>org.apache.xerces.xs</code> package.</p>
      <p>[schema information] property is only available on the
	<code>endElement</code> method for the validation root. When this method
	is called, information about various components can be retrieved by</p>
      <source>import org.apache.xerces.xs.*;

...

public void endElement(QName element, Augmentations augs) {
    ElementPSVI elemPSVI = (ElementPSVI)augs.getItem("ELEMENT_PSVI");
    XSModel xsModel = elemPSVI.getSchemaInformation();
    // get a list of [namespace schema information information item]s,
    // one for each namespace.
    XSNamespaceItemList nsItems = xsModel.getNamespaceItems();
    ...
    
    // get an element declaration of the specified name and namespace
    XSElementDeclaration elemDecl = xsModel.getElementDeclaration
        (namespace, name);
    ...
}</source>
    </a>
  </faq>


  <faq title="Accessing PSVI via DOM">
    <q>How do I access PSVI via DOM?</q>  
    <a><anchor name="dom3-psvi"/><p>Use  
	the <link idref='properties' anchor="dom.document-class-name">http://apache.org/xml/properties/dom/document-class-name</link> property
 	to set <code>org.apache.xerces.dom.PSVIDocumentImpl</code> as the implementation 
        of the <code>org.w3c.dom.Document</code> interface. In the resulting DOM tree, you may cast 
        <code>org.w3c.dom.Element</code> to the 
        <code>org.apache.xerces.xs.ElementPSVI</code> and  
        <code>org.w3c.dom.Attr</code> to the 
        <code>org.apache.xerces.xs.AttributePSVI</code>. 
      </p>
      <source>import org.apache.xerces.xs.ElementPSVI;
import org.apache.xerces.xs.XSModel;
import org.apache.xerces.xs.XSNamedMap;

...

Document document = parser.getDocument();
Element root = document.getDocumentElement();

// retrieve PSVI for the root element
ElementPSVI rootPSVI = (ElementPSVI)root;

// retrieve the schema used in validation of this document
XSModel schema = rootPSVI.getSchemaInformation();
XSNamedMap elementDeclarations =
    schema.getComponents(XSConstants.ELEMENT_DECLARATION);

// get schema normalized value
String normalizedValue = rootPSVI.getSchemaNormalizedValue();</source>
    </a>
  </faq>


  <faq title="Accessing PSVI via SAX">
    <q>How do I access PSVI via SAX?</q>
    <a> <p>The Xerces SAX parser also implements the
	<code>org.apache.xerces.xs.PSVIProvider</code> interface.
	Within the scope of the methods handling the start 
	(<code>org.xml.sax.ContentHandler.startElement</code>) and 
	end (<code>org.xml.sax.ContentHandler.endElement</code>) of an element, 
	applications may use the <code>PSVIProvider</code> to retrieve the PSVI 
	related to the element and its attributes.
      </p>
      <source>import org.apache.xerces.xs.PSVIProvider;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

...

SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();
XMLReader reader = parser.getXMLReader();
PSVIProvider psviProvider = (PSVIProvider)reader;</source>
    </a>
  </faq>

 <faq title="Accessing PSVI via the JAXP 1.4 Validation API">
   <q>How do I access PSVI via the JAXP 1.4 Validation API?</q>
   <a> <p>Like the Xerces SAX parser the implementations of <code>javax.xml.validation.Validator</code>
       and <code>javax.xml.validation.ValidatorHandler</code> also implement the
       <code>org.apache.xerces.xs.PSVIProvider</code> interface. Within the scope of the methods 
       handling the start (<code>org.xml.sax.ContentHandler.startElement</code>) and end 
       (<code>org.xml.sax.ContentHandler.endElement</code>) of an element, applications may use 
       the <code>PSVIProvider</code> to retrieve the PSVI related to the element and its attributes.</p>
   </a>
 </faq>
  
  <faq title="Parsing and analyzing an XML schema">
    <q>How do I parse and analyze an XML schema?</q>
    <a> <p>Please, refer to the <link idref='faq-grammars'>Examining Grammars</link> FAQ.</p>
    </a>
  </faq>

 <faq title="Using XSLoader to get an XSModel">
  <q>Can I parse and query XML Schema components in memory?</q>
  <a>
   <p>
       Yes, the <jump href="http://www.w3.org/Submission/2004/SUBM-xmlschema-api-20040309/">XML Schema API</jump>
       specification defines an interface called <code>XSLoader</code> which provides methods 
       for loading XML Schema documents into an <code>XSModel</code>. The <code>XSImplementation</code>
       interface provides a method to create an <code>XSLoader</code> using the 
       <jump href="http://www.w3.org/TR/2003/CR-DOM-Level-3-Core-20031107/core.html#Bootstrap">
       DOM Level 3 Bootstraping mechanism</jump>. An application can get a reference to 
       an <code>XSImplementation</code> using the <code>getDOMImplementation</code> method 
       on the <code>DOMImplementationRegistry</code> object with the feature string "XS-Loader".
       To create an <code>XSLoader</code> you need to do something like this:
   </p>
   <source>import org.w3c.dom.DOMImplementationRegistry;
import org.apache.xerces.xs.XSImplementation;
import org.apache.xerces.xs.XSLoader; 

...
   
// Get DOM Implementation using DOM Registry
System.setProperty(DOMImplementationRegistry.PROPERTY,
    "org.apache.xerces.dom.DOMXSImplementationSourceImpl");
DOMImplementationRegistry registry = DOMImplementationRegistry.newInstance();

XSImplementation impl = 
    (XSImplementation) registry.getDOMImplementation("XS-Loader");

XSLoader schemaLoader = impl.createXSLoader(null);

...</source>
  </a>
 </faq>
</faqs>
