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<!DOCTYPE s1 SYSTEM "sbk:/style/dtd/document.dtd">
<s1 title="XML Schema Support">
<s2 title="Introduction">
<p>&XercesCName; includes an implementation of the W3C XML Schema
specification, a recommendation of the Worldwide Web Consortium
available in three parts:
<jump href="http://www.w3.org/TR/xmlschema-0/">XML Schema: Primer</jump>,
<jump href="http://www.w3.org/TR/xmlschema-1/">XML Schema: Structures</jump> and
<jump href="http://www.w3.org/TR/xmlschema-2/">XML Schema: Datatypes</jump>.
We consider this implementation complete except for the limitations outlined below.
</p>
</s2>
<anchor name="limitation"/>
<s2 title="Limitations">
<ul>
<li>In certain complex content models specifying large
values for the <code>minOccurs</code> or <code>maxOccurs</code>
attributes may result in poor performance and/or large amount
of memory being allocated by the parser. In such situations large values for
<code>minOccurs</code> should be avoided, and <code>unbounded</code>
should be used instead.</li>
<li>The parser treats local elements in the same scope with the
same name and namespace as one element declaration and does not
differentiate between them.</li>
</ul>
</s2>
<anchor name="interpretation"/>
<s2 title="Interpretation of Areas that are Unclear or Implementation-Dependent">
<s3 title="keyref">
<p>
We have interpreted the specs as requiring <keyref> Identity Constraints to refer to
<key> or <unique> identity constraints within the scope of the elements to which
the <keyref> is attached. This interpretation is at variance with the Schema Primer, which
contains an example with a <keyref> declared on an element used inside the element of its
corresponding <key>.
</p>
</s3>
<s3 title="out-of-bound float values">
<p>
For float data, the specification does not explicitly prescribe how to deal with
out-of-bound data. &XercesCName; converts these values as shown below:
</p>
<table>
<tr>
<td>Values in range</td>
<td>Values converted</td>
</tr>
<tr>
<td>less than -2<sup>24</sup> * 2<sup>104</sup> (approx -3.402823669e+38) </td>
<td>-INF</td>
</tr>
<tr>
<td>greater than -1 * 2<sup>-149</sup> (approx -1.401298464e-45) and less than -0 </td>
<td>-0</td>
</tr>
<tr>
<td>greater than +0 and less than +1 * 2<sup>-149</sup> (approx +1.401298464e-45) </td>
<td>+0</td>
</tr>
<tr>
<td>greater than +2<sup>24</sup> * 2<sup>104</sup> (approx 3.402823669e+38) </td>
<td>+INF</td>
</tr>
</table>
<p>
The effect of this conversion would invalidate an instance data, for example,
"1.1e-46", of a data type derived from float, with minExclusive value '+0',
since "1.1e-46" is converted to "+0", which is the same as the minExclusive.
</p>
</s3>
<s3 title="out-of-bound double values">
<p>
Similarly, &XercesCName; converts double values as shown below (the values
depend on the system specific values of DBL_MAX and DBL_MIN):
</p>
<table>
<tr>
<td>Values in range</td>
<td>Values converted</td>
</tr>
<tr>
<td>less than -DBL_MAX (approx -1.7976931348623158e+308) </td>
<td>-INF</td>
</tr>
<tr>
<td>greater than -DBL_MIN (approx -2.2250738585072014e-308) and less than -0 </td>
<td>-0</td>
</tr>
<tr>
<td>greater than +0 and less than +DBL_MIN (approx +2.2250738585072014e-308) </td>
<td>+0</td>
</tr>
<tr>
<td>greater than +DBL_MAX (approx +1.7976931348623158e+308) </td>
<td>+INF</td>
</tr>
</table>
</s3>
</s2>
<anchor name="usage"/>
<s2 title="Usage">
<p>Below is an example that shows how to turn on schema processing in DOMParser
(default is off). Note that you must also turn on namespace support
(default is off) for schema processing.
</p>
<source>// Instantiate the DOM parser.
XercesDOMParser parser;
parser.setDoNamespaces(true);
parser.setDoSchema(true);
parser.parse(xmlFile);
</source>
<p>Usage in SAXParser is similar, please refer to the SAXCount
sample program for further reference.
</p>
<p>Below is an example that shows how to turn on schema processing in SAX2XMLReader
(default is on). Note that namespace must be on (default is on) as well.
</p>
<source>SAX2XMLReader* parser = XMLReaderFactory::createXMLReader();
parser->setFeature(XMLUni::fgSAX2CoreNameSpaces, true);
parser->setFeature(XMLUni::fgXercesSchema, true);
parser->parse(xmlFile);
</source>
</s2>
<anchor name="associate"/>
<s2 title="Associating Schema Grammar with instance document">
<p>Schema grammars can be associated with instance documents in three ways.
</p>
<s3 title="Specifying Schema Grammar through attributes in the instance document">
<p>If schema grammar was not specified externally through methods,
then each instance 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 xsi:noNamespaceSchemaLocation attribute otherwise.
</p>
<p>Here is an example with no target namespace:
</p>
<source><?xml version="1.0" encoding="UTF-8"?>
<personnel xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation='personal.xsd'>
...
</personnel>
</source>
<p>Here is an example with a target namespace. Note that it is an error to specify a
different namespace in xsi:schemaLocation attribute than the target namespace
defined in the Schema.
</p>
<source><?xml version="1.0" encoding="UTF-8"?>
<personnel xmlns="http://my.com"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://my.com personal.xsd http://my2.com test2.xsd">
...
</personnel>
</source>
</s3>
<s3 title="Specifying Schema Grammar through method calls">
<p>An application developer may associate schemas with instance documents through
methods <code>setExternalSchemaLocation</code> if they use namespaces, and
<code>setExternalNoNamespaceSchemaLocation</code> otherwise.
(For SAX2XMLReader, use the properties:
"http://apache.org/xml/properties/schema/external-schemaLocation" and
"http://apache.org/xml/properties/schema/external-noNamespaceSchemaLocation")
</p>
<p>Here is an example with no target namespace:
</p>
<source>
// Instantiate the DOM parser.
XercesDOMParser parser;
parser.setDoNamespaces(true);
parser.setDoSchema(true);
parser.setExternalNoNamespaceSchemaLocation("personal.xsd");
parser.parse("test.xml");
// Instantiate the SAX2 XMLReader.
SAX2XMLReader* parser = XMLReaderFactory::createXMLReader();
XMLCh* propertyValue = XMLString::transcode("personal.xsd");
ArrayJanitor<XMLCh> janValue(propertyValue);
parser->setProperty(
XMLUni::fgXercesSchemaExternalNoNameSpaceSchemaLocation,
propertyValue);
parser.parse("test.xml");
</source>
<p>Here is an example with a target namespace. Note that it is an error to specify a
different namespace in <code>setExternalSchemaLocation</code> than the target
namespace defined in the Schema.
</p>
<source>
// Instantiate the DOM parser.
XercesDOMParser parser;
parser.setDoNamespaces(true);
parser.setDoSchema(true);
parser.setExternalSchemaLocation(
"http://my.com personal.xsd http://my2.com test2.xsd");
parser.parse("test.xml");
// Instantiate the SAX2 XMLReader.
SAX2XMLReader* parser = XMLReaderFactory::createXMLReader();
XMLCh* propertyValue = XMLString::transcode(
"http://my.com personal.xsd http://my2.com test2.xsd");
ArrayJanitor<XMLCh> janValue(propertyValue);
parser->setProperty(
XMLUni::fgXercesSchemaExternalSchemaLocation,
propertyValue);
parser.parse("test.xml");
</source>
</s3>
<s3 title="Pre-parsing and Caching Schema Grammar">
<p>An application developer may also pre-parse and
cache the grammar corresponding to the XML document
namespace as described in the
<jump href="program-others-&XercesC3Series;.html#GrammarCache">Pre-parsing
Grammar and Grammar Caching</jump> section of the
&XercesCName; Programming Guide.</p>
</s3>
</s2>
</s1>
