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<h1>13. XML Support</h1>
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<h2>13.10. XMLType</h2>
<p>
XMLType is a predefined type for representing XML entities as UDT objects.
This is compatible with Oracle9i and later.
You can get better performance and flexibility by using use plain built-in functions
that directly operate with XML entities.
All predefined member functions of XMLType for extracting fragments from
an XMLType are actually wrappers for <a href="fn_xpath_eval.html">xpath_eval()</a> built-in function.
You can declare a column of XMLType but the actual type of the created column will be "LONG XML".
Thus any XML-related feature that can be used for "LONG XML" column will work with XMLType.
E.g. <a href="CREATETABLE.html#sqlrefcreattablewithschema">WITH SCHEMA constraint</a> allows you to force stored values
to match a particular schema; <a href="queryingxmldata.html#usingxmlfreetext">XML free text index</a> can accelerate search for documents by content
etc.
</p>
<p>
XMLType behaves like any user-defined type, with the only difference in type conversion rules.
If an XML entity is passed as an argument instead of an instance of XMLType, a new instance of
XMLType is created by a constructor that takes the entity as an argument.
Similarly, functions that accept XML entities as arguments can also accept an instance of
XMLType as an actual value of argument.
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<p>
The following example creates a table with an XMLType column, put two records there
and performs a simple search:</p>
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<pre class="screen">
CREATE TABLE Xml_tab ( xmlval XMLType);
INSERT INTO Xml_tab VALUES (
xmltype('<?xml version="1.0"?>
<EMP>
<EMPNO>221</EMPNO>
<ENAME>John</ENAME>
</EMP>'));
INSERT INTO Xml_tab VALUES (
xmltype('<?xml version="1.0"?>
<PO>
<PONO>331</PONO>
<PONAME>PO_1</PONAME>
</PO>'));
-- now extract the numerical values for the employee numbers
SELECT e.xmlval.extract('//EMPNO/text()').getNumVal() as empno
FROM Xml_tab
WHERE e.xmlval.existsnode('/EMP/EMPNO') = 1;
</pre>
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<p>To create a new instance of XMLType, the constructor <a href="fn_XMLType.XMLType.html">XMLType()</a>
or a function <a href="fn_createXML.html">createXML()</a> is used.
</p>
<p>
Virtuoso can perform XPATH search in XMLType instances:
<a href="fn_XMLType.extract.html">extract()</a>
and
<a href="fn_XMLType.existsNode.html">existsNode()</a>
member functions are convenient for simple searches and any
built-in XPATH functions like
<a href="fn_xpath_eval.html">xpath_eval()</a> or
<a href="fn_xquery_eval.html">xquery_eval()</a> can handle
XMLType parameters instead of XML entity parameters.
An application can use
<a href="fn_XMLType.getStringVal.html">getStringVal()</a>,
<a href="fn_XMLType.getNumVal.html">getNumVal()</a> and
<a href="fn_XMLType.getClobVal.html">getColbVal()</a>
member functions to convert found node to strings, numbers or an XML source text of the node.
</p>
<p>Instances of the type can store the URL of the XML schema to which they should conform.
This URL can be specified when an instance is constructed;
Once an instance is created, its schema URL cannot be changed but a modified copy can be created by
<a href="fn_XMLType.createSchemaBasedXML.html">createSchemaBasedXML()</a>
and
<a href="fn_XMLType.createNonSchemaBasedXML.html">createNonSchemaBasedXML()</a>
member functions;
<a href="fn_XMLType.isSchemaBased.html">isSchemaBased()</a>
and <a href="fn_XMLType.getSchemaURL.html">getSchemaURL()</a>
member functions check whether the given instance is schema based or not and
what particular schema is used.
</p>
<p>
An schema based XMLType instance can be validated against its schema;
If it has been validated against its schema once with no errors detected then
a special "VALIDATED" flag is set
in the instance indicating that there is no need to validate it again.
<a href="fn_XMLType.schemaValidate.html">schemaValidate()</a>
member function performs the validation,
<a href="fn_XMLType.isSchemaValidated.html">isSchemaValidated()</a>
queries the "VALIDATED" flag and
<a href="fn_XMLType.setSchemaValidated.html">setSchemaValidated()</a>
changes the "VALIDATED" flag if application needs optimization tricks.
</p>
<p>
In addition, any instance can be validated against an arbitrary schema via member function
<a href="fn_XMLType.isSchemaValid.html">isSchemaValid()</a>.
Built-in function <a href="">xml_validate_schema()</a>
may accept instance of XMLType as its first argument, providing even more
validation functionality.
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