| Oracle® XML DB Developer's Guide 11g Release 2 (11.2) Part Number E10492-02 |
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| Oracle® XML DB Developer's Guide 11g Release 2 (11.2) Part Number E10492-02 |
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View PDF |
This chapter describes the SQL functions and XMLType APIs for transforming XMLType data using XSLT style sheets. It also explains the various functions and APIs available for validating the XMLType instance against an XML schema.
This chapter contains these topics:
XML documents have structure but no format. To add format to the XML documents you can use Extensible Stylesheet Language (XSL). XSL provides a way of displaying XML semantics. It can map XML elements into other formatting or mark-up languages such as HTML.
In Oracle XML DB, XMLType instances or XML data stored in XMLType tables, columns, or views in Oracle Database, can be (formatted) transformed into HTML, XML, and other mark-up languages, using XSL style sheets and XMLType method transform(). This process conforms to the W3C XSL Transformations 1.0 Recommendation.
XMLType instance can be transformed in the following ways:
Using Oracle SQL function XMLtransform or XMLType method transform() in the database.
Using XDK transformation options in the middle tier, such as XSLT Processor for Java.
Note:
PL/SQL package
DBMS_XSLPROCESSOR provides a convenient and efficient way of applying a single style sheet to multiple documents. The performance of this package is better than that of method transform(), because the style sheet is parsed only once.See Also:
Chapter 3, "Using Oracle XML DB", the section, "XSL Transformation and Oracle XML DB"
Oracle XML Developer's Kit Programmer's Guide, the chapter on XSQL Pages Publishing Framework
Figure 11-1 shows the syntax of Oracle SQL function XMLtransform. This function takes as arguments an XMLType instance and an XSLT style sheet. The style sheet can be an XMLType instance or a VARCHAR2 string literal. It applies the style sheet to the instance and returns an XMLType instance.
You can alternatively use XMLType method transform() as an alternative to Oracle SQL function XMLtransform; it has the same functionality.
Figure 11-2 shows how XMLtransform transforms an XML document by using an XSLT style sheet. It returns the processed output as XML, HTML, and so on, as specified by the XSLT style sheet. You typically use XMLtransform when retrieving or generating XML documents stored as XMLType in the database.
The examples in this section illustrate how to use Oracle SQL function XMLtransform and XMLType method transform() to transform XML data stored as XMLType to various formats.
Example 11-1 sets up an XML schema and tables that are needed to run other examples in this chapter. The call to deleteSchema here ensures that there is no existing XML schema before creating one. If no such schema exists, then deleteSchema produces an error.
Example 11-1 Registering XML Schema and Inserting XML Data
BEGIN
-- Delete the schema, if it already exists.
DBMS_XMLSCHEMA.deleteSchema('http://www.example.com/schemas/ipo.xsd',4);
END;
/
BEGIN
-- Register the schema
DBMS_XMLSCHEMA.registerSchema(
'http://www.example.com/schemas/ipo.xsd',
'<schema targetNamespace="http://www.example.com/IPO"
xmlns="http://www.w3.org/2001/XMLSchema"
xmlns:ipo="http://www.example.com/IPO">
<!-- annotation>
<documentation xml:lang="en">
International Purchase order schema for Example.com
Copyright 2000 Example.com. All rights reserved.
</documentation>
</annotation -->
<element name="purchaseOrder" type="ipo:PurchaseOrderType"/>
<element name="comment" type="string"/>
<complexType name="PurchaseOrderType">
<sequence>
<element name="shipTo" type="ipo:Address"/>
<element name="billTo" type="ipo:Address"/>
<element ref="ipo:comment" minOccurs="0"/>
<element name="items" type="ipo:Items"/>
</sequence>
<attribute name="orderDate" type="date"/>
</complexType>
<complexType name="Items">
<sequence>
<element name="item" minOccurs="0" maxOccurs="unbounded">
<complexType>
<sequence>
<element name="productName" type="string"/>
<element name="quantity">
<simpleType>
<restriction base="positiveInteger">
<maxExclusive value="100"/>
</restriction>
</simpleType>
</element>
<element name="USPrice" type="decimal"/>
<element ref="ipo:comment" minOccurs="0"/>
<element name="shipDate" type="date" minOccurs="0"/>
</sequence>
<attribute name="partNum" type="ipo:SKU" use="required"/>
</complexType>
</element>
</sequence>
</complexType>
<complexType name="Address">
<sequence>
<element name="name" type="string"/>
<element name="street" type="string"/>
<element name="city" type="string"/>
<element name="state" type="string"/>
<element name="country" type="string"/>
<element name="zip" type="string"/>
</sequence>
</complexType>
<simpleType name="SKU">
<restriction base="string">
<pattern value="[0-9]{3}-[A-Z]{2}"/>
</restriction>
</simpleType>
</schema>',
TRUE,
TRUE,
FALSE);
END;
/
-- Create table to hold XML instance documents
DROP TABLE po_tab;
CREATE TABLE po_tab (id NUMBER, xmlcol XMLType)
XMLType COLUMN xmlcol
XMLSCHEMA "http://www.example.com/schemas/ipo.xsd"
ELEMENT "purchaseOrder";
INSERT INTO po_tab
VALUES(1, XMLType(
'<?xml version="1.0"?>
<ipo:purchaseOrder
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ipo="http://www.example.com/IPO"
xsi:schemaLocation="http://www.example.com/IPO
http://www.example.com/schemas/ipo.xsd"
orderDate="1999-12-01">
<shipTo>
<name>Helen Zoe</name>
<street>121 Broadway</street>
<city>Cardiff</city>
<state>Wales</state>
<country>UK</country>
<zip>CF2 1QJ</zip>
</shipTo>
<billTo>
<name>Robert Smith</name>
<street>8 Oak Avenue</street>
<city>Old Town</city>
<state>CA</state>
<country>US</country>
<zip>95819</zip>
</billTo>
<items>
<item partNum="833-AA">
<productName>Lapis necklace</productName>
<quantity>1</quantity>
<USPrice>99.95</USPrice>
<ipo:comment>Want this for the holidays!</ipo:comment>
<shipDate>1999-12-05</shipDate>
</item>
</items>
</ipo:purchaseOrder>'));
Example 11-2 shows how to retrieve a style sheet using Oracle SQL function XMLtransform and DBURIType. See Chapter 20, "Accessing Data Through URIs" for information about DBURIType.
Example 11-2 Retrieving a Style Sheet using XMLTRANSFORM and DBURITYPE
DROP TABLE stylesheet_tab;
CREATE TABLE stylesheet_tab (id NUMBER, stylesheet XMLType);
INSERT INTO stylesheet_tab
VALUES (1,
XMLType(
'<?xml version="1.0" ?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="*">
<td>
<xsl:choose>
<xsl:when test="count(child::*) > 1">
<xsl:call-template name="nested"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="name(.)"/>:<xsl:value-of
select="text()"/>
</xsl:otherwise>
</xsl:choose>
</td>
</xsl:template>
<xsl:template match="*" name="nested" priority="-1" mode="nested2">
<b>
<!-- xsl:value-of select="count(child::*)"/ -->
<xsl:choose>
<xsl:when test="count(child::*) > 1">
<xsl:value-of select="name(.)"/>:<xsl:apply-templates
mode="nested2"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="name(.)"/>:<xsl:value-of
select="text()"/>
</xsl:otherwise>
</xsl:choose>
</b>
</xsl:template>
</xsl:stylesheet>'));
SELECT XMLSerialize(DOCUMENT XMLtransform(x.xmlcol, y.stylesheet)
AS varchar2(1000))
AS result FROM po_tab x, stylesheet_tab y WHERE y.id = 1;
This produces the following output (pretty-printed here for readability):
RESULT
---------------------------------------------------------
<td>
<b>ipo:purchaseOrder:
<b>shipTo:
<b>name:Helen Zoe</b>
<b>street:100 Broadway</b>
<b>city:Cardiff</b>
<b>state:Wales</b>
<b>country:UK</b>
<b>zip:CF2 1QJ</b>
</b>
<b>billTo:
<b>name:Robert Smith</b>
<b>street:8 Oak Avenue</b>
<b>city:Old Town</b>
<b>state:CA</b>
<b>country:US</b>
<b>zip:95819</b>
</b>
<b>items:</b>
</b>
</td>
Example 11-3 illustrates the use of a stored style sheet to transform XMLType instances. Unlike Example 11-2, Example 11-3 uses a scalar subquery to retrieve the stored style sheet.
Example 11-3 Retrieving a Style Sheet using XMLTRANSFORM and a Subquery
SELECT XMLSerialize(DOCUMENT
XMLtransform(
x.xmlcol,
(SELECT stylesheet FROM stylesheet_tab WHERE id = 1))
AS VARCHAR2(1000))
AS result FROM po_tab x;
Example 11-4 uses XMLType method transform() to transform an XMLType instance using a transient style sheet.
Example 11-4 Using Method TRANSFORM() with a Transient Style Sheet
SELECT XMLSerialize(
DOCUMENT
x.xmlcol.transform(
XMLType('<?xml version="1.0" ?>
<xsl:stylesheet
version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="*">
<td>
<xsl:choose>
<xsl:when test="count(child::*) > 1">
<xsl:call-template name="nested"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of
select =
"name(.)"/>:<xsl:value-of select="text()"/>
</xsl:otherwise>
</xsl:choose>
</td>
</xsl:template>
<xsl:template match="*" name="nested" priority="-1"
mode="nested2">
<b>
<!-- xsl:value-of select="count(child::*)"/ -->
<xsl:choose>
<xsl:when test="count(child::*) > 1">
<xsl:value-of select="name(.)"/>:
<xsl:apply-templates mode="nested2"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of
select =
"name(.)"/>:<xsl:value-of select="text()"/>
</xsl:otherwise>
</xsl:choose>
</b>
</xsl:template>
</xsl:stylesheet>'))
AS varchar2(1000))
FROM po_tab x;
Often, besides knowing whether a particular XML document is well-formed, you will need to know whether it conforms to a given XML schema, that is, whether it is valid with respect to that XML schema.
By default, the database checks to ensure that XMLType instances are well-formed. In addition, for XML schema-based XMLType instances, the database performs a few basic validation checks. Because full XML schema validation is an expensive operation, XMLType instances are not fully validated when they are constructed, stored, or retrieved.
You can use the following to validate and manipulate the recorded validation status of XML documents:
Oracle SQL function XMLIsValid and XMLType method IsSchemaValid() – Run the validation process unconditionally. Do not record any validation status. Return:
1 if the document is determined to be valid.
0 if the document is determined to be invalid or the validity of the document cannot be determined.
XMLType method SchemaValidate() – Runs the validation process if the validation status is 0, which it is by default. Sets the validation status to 1 if the document is determined to be valid. (Otherwise, the status remains 0.)
XMLType method isSchemaValidated() returns the recorded validation status of an XMLType instance.
XMLType method setSchemaValidated() sets (records) the validation status of an XMLType instance.
Note that the validation status indicates knowledge of validity, as follows:
1 means that the document is known to be valid.
0 means that validity of the document is unknown. The document might have been shown to be invalid during a validation check, but that invalidness is not recorded. A recorded validation status of 0 indicates only a lack of knowledge about the document's validity.
See Also:
Oracle Database SQL Language Reference for information about Oracle SQL function XMLIsValid
Oracle Database PL/SQL Packages and Types Reference for information about XMLType methods IsSchemaValid(), IsSchemaValidated(), SchemaValidate(), and setSchemaValidated()
The examples in this section illustrate how to use Oracle SQL function XMLIsValid and XMLType methods isSchemaValid() and schemaValidate() to validate XML data being stored as XMLType in Oracle XML DB.
Example 11-5 and Example 11-6 show how to validate an XML instance against an XML schema using PL/SQL method isSchemaValid().
Example 11-5 Validating XML using Method ISSCHEMAVALID() in SQL
SELECT x.xmlcol.isSchemaValid('http://www.example.com/schemas/ipo.xsd',
'purchaseOrder')
FROM po_tab x;
Example 11-6 Validating XML using Method ISSCHEMAVALID() in PL/SQL
DECLARE
xml_instance XMLType;
BEGIN
SELECT x.xmlcol INTO xml_instance FROM po_tab x WHERE id = 1;
IF xml_instance.isSchemaValid('http://www.example.com/schemas/ipo.xsd') = 0
THEN raise_application_error(-20500, 'Invalid Instance');
ELSE DBMS_OUTPUT.put_line('Instance is valid');
END IF;
END;
/
Instance is valid
PL/SQL procedure successfully completed.
XMLType method schemaValidate() can be used within INSERT and UPDATE triggers to ensure that all instances stored in the table are validated against the XML schema. Example 11-7 illustrates this.
Example 11-7 Validating XML using Method SCHEMAVALIDATE() within Triggers
DROP TABLE po_tab;
CREATE TABLE po_tab OF XMLType
XMLSCHEMA "http://www.example.com/schemas/ipo.xsd" ELEMENT "purchaseOrder";
CREATE TRIGGER emp_trig BEFORE INSERT OR UPDATE ON po_tab FOR EACH ROW
DECLARE
newxml XMLType;
BEGIn
newxml := :new.OBJECT_VALUE;
XMLTYPE.schemavalidate(newxml);
END;
/
Example 11-8 uses Oracle SQL function XMLIsValid to do the following:
Verify that the XMLType instance conforms to the specified XML schema
Ensure that the incoming XML documents are valid by using CHECK constraints
Example 11-8 Checking XML Validity using XMLISVALID within CHECK Constraints
DROP TABLE po_tab; CREATE TABLE po_tab OF XMLType (CHECK(XMLIsValid(OBJECT_VALUE) = 1)) XMLSCHEMA "http://www.example.com/schemas/ipo.xsd" ELEMENT "purchaseOrder";
Note:
The validation functions and procedures described in section "Validating XMLType Instances" facilitate validation checking. Of these,isSchemaValid is the only one that raises errors that indicate why validation has failed.
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