| Questions |

- Usage
- Using Entities and CDATA Sections
- XML Schema API
- Accessing PSVI via XNI
- Accessing PSVI via DOM
- Accessing PSVI via SAX
- Parsing and analyzing an XML schema

| Answers |

| How do I validate against XML schema? |

In this release, schema validation has been integrated with the regular SAXParser and DOMParser classes. No special classes are required to parse documents that use a schema.

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 XML Schema Part 1 section 4.3.2. Here is an example with no target namespace:

    <document
        xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
        xsi:noNamespaceSchemaLocation='document.xsd'>
        ...
    </document>

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.

    <document
        xmlns='http://my.com'
        xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
        xsi:schemaLocation='http://my.com document.xsd'>
        ...
    </document>

Review the sample file, 'data/personal.xsd' for an example of an XML Schema grammar.

| How does XML Schema processor treats entities and CDATA secptions? |

According to the XML Infoset the infoset items contributing to the [character information item] 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]" (Appendix D) 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.

| Does Xerces provide access to the post schema validation infoset (PSVI)? |

Xerces defines a set of objects and interfaces for accessing and querying the post schema validation infoset (PSVI) defined in Contributions to the post-schema-validation infoset (Appendix C.2). The interfaces defined in the `org.apache.xerces.impl.xs.psvi` allow developers to access the XML Schema components, which follow as a consequence of validation and/or assessment. The interfaces defined in the `>org.apache.xerces.xni.psvi` defines a set of interfaces for accessing the PSVI from a document instance.

| The set of above interfaces is experimental and may change in the future.

| How do I access PSVI via XNI? |

From within an `XMLDocumentHandler`, one can retrieve PSVI information while in the scope of the document handler start/end element calls:

    import org.apache.xerces.xni.psvi.*;

    ...

    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();
        ...
    }

| For more information, please refer to the API documentation of the PSVI interfaces.

The above code shows how to retrieve PSVI information after elements/attributes are assessed. The other kind of information PSVI offers is the property [schema information]. This property exposes all schema components in the schema that's used for assessment. These components and the schema itself are represented by interfaces in the `org.apache.xerces.impl.xs.psvi` package.

[schema information] property is only available on the `endElement` method for the validation root. When this method is called, information about various components can be retrieved by

    import org.apache.xerces.xni.psvi.*;
    import org.apache.xerces.impl.xs.psvi.*;

    ...

    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.
        ObjectList nsItems = xsModel.getNamespaceItems();
        // get an element declaration of the specified name and namespace
        XSElementDeclaration elemDecl = xsModel.getElementDeclaration
            (name, namespace);
        ...
    }

| How do I access PSVI via DOM? |

Use http://apache.org/xml/properties/dom/document-class-name property to set `org.apache.xerces.dom.PSVIDocumentImpl` document interfaces implementation. In the resulting DOM tree, you may cast `org.w3c.dom.Element` to the `org.apache.xerces.xni.psvi.ElementPSVI` and `org.w3c.dom.Attr` to the `org.apache.xerces.xni.psvi.AttributePSVI`.

    import org.apache.xerces.xni.psvi.*;
    import org.apache.xerces.impl.xs.psvi.XSModel;
    import org.apache.xerces.impl.xs.psvi.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();

| How do I access PSVI via SAX? |

Xerces SAX parser also implements `org.apache.xerces.impl.xs.psvi.PSVIProvider` interface. Within the scope of the methods handling the start and end of an element, i.e. org.xml.sax.ContentHandler.startElement (..), an application can use the PSVIProvider to retrieve the PSVI related to that element and its attributes.

    import org.apache.xerces.impl.xs.psvi.PSVIProvider;
    import javax.xml.parsers.SAXParser;
    import javax.xml.parsers.SAXParserFactory;

    ...

    SAXParserFactory factory = SAXParserFactory.newInstance();
    SAXParser parser = factory.newSAXParser();
    PSVIProvider psviProvider = (PSVIProvider)parser;

| How do I parse and analyze an XML schema? |

| Please, refer to the Examining Grammars FAQ.

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