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| <reference id="rnmspc" xml:lang="en-us"> | |
| <title>XML namespaces</title> | |
| <titlealts> | |
| <searchtitle>XML namespaces</searchtitle> | |
| </titlealts> | |
| <shortdesc>An XML namespace is a collection of names, identified by a URI | |
| reference, which are used in XML documents as element types and attribute | |
| names.</shortdesc> | |
| <prolog><metadata> | |
| <keywords><indexterm>XML namespaces<indexterm>overview</indexterm></indexterm> | |
| </keywords> | |
| </metadata></prolog> | |
| <refbody> | |
| <section>XML namespaces are defined by a W3C recommendation, dating 16 August | |
| 2006, called <xref format="html" href="http://www.w3.org/TR/2006/REC-xml-names-20060816/" | |
| scope="external">Namespaces in XML</xref>. XML tag names should be globally | |
| unique, as well as short for performance reasons. In order to resolve this | |
| conflict, the W3C namespace recommendation defines an attribute <b>xmlns</b> which | |
| can amend any XML element. If it is present in an element, it identifies the | |
| namespace for this element.</section> | |
| <section><p>The xmlns attribute has the following syntax:</p><p><codeph>xmlns:<varname>prefix</varname>=namespace</codeph> </p><p>where <codeph>namespace</codeph | |
| > is a unique URI (such as www.ibm.com) and where <codeph><varname>prefix</varname></codeph> represents | |
| the namespace and provides a pointer to it.</p><p>In the following customer | |
| element definition, an accounting namespace is defined in order to be able | |
| to distinguish the element tags from those appearing in customer records created | |
| by other business applications:</p><p><codeblock><acct:customer xmlns:acct="http://www.my.com/acct-REV10"> | |
| <acct:name>Corporation</acct:name> | |
| <acct:order acct:ref="5566"/> | |
| <acct:status>invoice</acct:status> | |
| </acct:customer> </codeblock> </p><p>The namespace definition in the first | |
| line assigns the namespace http://www.my.com/acct-REV10 to the prefix. This | |
| prefix is used on the element names such as name in order to attach them to | |
| the namespace. A second application, for example, a fulfillment system, can | |
| assign a different namespace to its customer elements:</p><p><codeblock><ful:customer xmlns:ful="http://www.your.com/ful"> | |
| <ful:name>Corporation</ful:name> | |
| <ful:order ful:ref="A98756"/> | |
| <ful:status>shipped</ful:status> | |
| </ful:customer></codeblock> </p><p>An application processing both data | |
| structures is now able to treat the accounting and the fulfillment data differently. | |
| There is a default namespace. It is set if no local name is assigned in the | |
| namespace definition:</p><p><codeblock><acct:customer xmlns="http://www.my.com/acct-REV10" xmlns:acct="http://www.my.com/acct-REV10 "> | |
| <name>Corporation</name> | |
| <order acct:ref="5566"/> | |
| <status>invoice</status> | |
| </customer></codeblock></p><p>In this example, all tags in the customer | |
| record are qualified to reside in the namespace http://www.my.com/acct-REV10. | |
| No explicit prefix is needed because the default namespace is used. Note that | |
| the default namespace applies to any attributes definitions.</p></section> | |
| <section><title>XML schemas and namespaces</title><p>In the following XML | |
| schema, the default namespace for the schema is defined as the standard XML | |
| schema namespace http://www.w3.org/2001/XMLSchema; there is also a schema | |
| specific namespace http://www.ibm.com.</p><p><codeblock><?xml version="1.0"?> | |
| <schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns:TestSchema="http://www.ibm.com"> | |
| <simpleType name="ZipCodeType"> | |
| <restriction base="integer"> | |
| <minInclusive value="10000"/> | |
| <maxInclusive value="99999"/> | |
| </restriction> | |
| </simpleType> | |
| <!--element definitions skipped --> | |
| </schema> </codeblock></p><p>Assuming that the preceding XML schema is | |
| saved as <filepath>C:\temp\TestSchema.xsd</filepath>, a sample XML file that | |
| validates against this schema is:</p><p><codeblock><?xml version="1.0"?> | |
| <x:addressList xmlns:x="http://www.ibm.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.ibm.com file:///C:/temp/TestSchema.xsd"> | |
| xsi:schemaLocation="http://www.ibm.com file:///C:/temp/TestSchema.xsd"> | |
| <x:address> | |
| <x:street>x:Vangerowstrasse</x:street> | |
| <x:zipCode>69115</x:zipCode> | |
| <x:city>x:Heidelberg</x:city> | |
| </x:address> | |
| <x:address> | |
| <x:street>x:Bernal Road</x:street> | |
| <x:zipCode>90375</x:zipCode> | |
| <x:city>x:San Jose</x:city> | |
| </x:address> | |
| </x:addressList> </codeblock></p></section> | |
| <section><title>Target namespace</title><p> The target namespace serves to | |
| identify the namespace within which the association between the element and | |
| its name exists. In the case of declarations, this association determines | |
| the namespace of the elements in XML files conforming to the schema. An XML | |
| file importing a schema must reference its target namespace in the schemaLocation | |
| attribute. Any mismatches between the target and the actual namespace of an | |
| element are reported as schema validation errors. In our example, the target | |
| namespace is http://www.ibm.com; it is defined in the XML schema file and | |
| referenced twice in the XML file. Any mismatch between these three occurrences | |
| of the namespace lead to validation errors.</p><p> The following examples | |
| show how target namespaces and namespace prefixes work in XML schemas and | |
| their corresponding XML instance documents.</p></section> | |
| <section><title>Sample 1 - A schema with both a default and target namespace | |
| and unqualified locals</title><p>The XML schema: </p><p><codeblock><?xml version="1.0"?> | |
| <schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns:x="http://www.ibm.com"> | |
| <complexType name="AddressType"> | |
| <sequence> | |
| <element name="name" type="string"></element> | |
| </sequence> | |
| </complexType> | |
| <element name="MyAddress" type="x:AddressType"></element> | |
| </schema> </codeblock> </p><p>A valid XML instance document created from | |
| this schema looks like this. Local elements and attributes are unqualified.</p><p><codeblock><?xml version="1.0"?> | |
| <x:MyAddress xmlns:x="http://www.ibm.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.ibm.com x.xsd "> | |
| <name>Peter Smith</name> | |
| </x:MyAddress> </codeblock></p><p>When local elements (such as the "name" | |
| element) and attributes are unqualified in an XML file, then only the root | |
| element is qualified. So, in this example, the "x" namespace prefix is assigned | |
| to the root element "MyAddress", associating it with the namespace "http://www.ibm.com", | |
| but the"x" prefix is not assigned to the local element "name".</p></section> | |
| <section><title>Sample 2 - A schema with both a default and target namespace | |
| and qualified locals</title><p><codeblock><?xml version="1.0"?> | |
| <schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns:x="http://www.ibm.com" elementFormDefault="qualified"> | |
| <complexType name="AddressType"> | |
| <sequence> | |
| <element name="name" type="string"></element> | |
| </sequence> | |
| </complexType> | |
| <element name="MyAddress" type="x:AddressType"></element> | |
| </schema> </codeblock></p><p>A valid XML instance document created from | |
| this schema looks like this. Local elements and attributes are qualified This | |
| is because the elementFormDefault attribute is set to qualified in the XML | |
| schema.</p><p><codeblock><?xml version="1.0"?> | |
| <x:MyAddress xmlns:x="http://www.ibm.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" | |
| xsi:schemaLocation="http://www.ibm.com x.xsd "> | |
| <x:name>Peter Smith</x:name> | |
| </x:MyAddress></codeblock> </p><p>In this example, the "x" namespace prefix | |
| is assigned to both the root element "MyAddress" and the local element "name", | |
| associating them with the namespace "http://www.ibm.com",.</p></section> | |
| <section><title>Sample 3 - Schema with target Namespace, and explicitly defines | |
| xmlns:xsd</title><p>This XML schema adds this attribute: </p><codeph>xmlns:xsd="http://www.w3.org/2001/XMLSchema </codeph><p>What | |
| this means is that each of the constructs that are defined by the XML schema | |
| language will need to be qualified with the "xsd" prefix. For example, xsd:complexType | |
| and xsd:string</p><p>. Note that you can chose any other prefixes such as | |
| "xs" or "foobar" in your declaration and usage.</p><p>You can specify this | |
| prefix in the XML schema preferences page. For more information, refer to | |
| the related tasks.</p><p>All user defined types belong to the namespace http://www.ibm.com | |
| as defined by the targetNamespace attribute, and the prefix is "x" as defined | |
| by the xmlns:x attribute.</p><p><codeblock><?xml version="1.0"?> | |
| <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns:x="http://www.ibm.com"> | |
| <xsd:complexType name="AddressType"> | |
| <xsd:sequence> | |
| <xsd:element name="name" type="xsd:string"></xsd:element> | |
| </xsd:sequence> | |
| </xsd:complexType> | |
| <xsd:element name="MyAddress" type="x:AddressType"></xsd:element> | |
| </xsd:schema></codeblock> </p><p>A valid XML instance document created | |
| from this schema looks like this. Local elements and attributes are unqualified. | |
| The semantics of qualification is the same as Sample 1.</p><p><codeblock><?xml version="1.0"?> | |
| <x:MyAddress xmlns:x="http://www.ibm.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.ibm.com x.xsd "> | |
| <name>Peter Smith</name> | |
| </x:MyAddress></codeblock></p></section> | |
| <section><title>Sample 4 - Schema with undeclared target Namespace that explicitly | |
| defines xmlns:xsd</title><p>This XML schema has no target namespace for itself. | |
| In this case, it is highly recommended that all XML schema constructs be explicitly | |
| qualified with a prefix such as "xsd". The definitions and declarations from | |
| this schema such as AddressType are referenced without namespace qualification | |
| since there is no namespace prefix. </p><p><codeblock><?xml version="1.0"?> | |
| <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> | |
| <xsd:complexType name="AddressType"> | |
| <xsd:sequence> | |
| <xsd:element name="name" type="xsd:string"></xsd:element> | |
| <xsd:element name="name" type="xsd:string"></xsd:element> | |
| <xsd:element name="name" type="xsd:string"></xsd:element> | |
| </xsd:sequence> | |
| </xsd:complexType> | |
| <xsd:element name="MyAddress" type="AddressType"></xsd:element> | |
| </xsd:schema> </codeblock></p><p>A valid XML instance document created | |
| from the schema looks like this. All elements are unqualified.</p><p><codeblock><?xml version="1.0"?> | |
| <MyAddress xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="x.xsd"> | |
| <name>name</name> | |
| </MyAddress></codeblock> </p></section> | |
| <section><title>Sample 5 - A schema where the target namespace is the default | |
| namespace</title><p>This is an XML schema where the target namespace is the | |
| default namespace. As well, the namespace has no namespace prefix.</p><p><codeblock><?xml version="1.0"?> | |
| <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns="http://www.ibm.com"> | |
| <xsd:complexType name="AddressType"> | |
| <xsd:sequence> | |
| <xsd:element name="name" type="xsd:string"></xsd:element> | |
| </xsd:sequence> | |
| </xsd:complexType> | |
| <xsd:element name="MyAddress" type="AddressType"></xsd:element> | |
| </xsd:schema> </codeblock> </p><p>A valid XML instance document created | |
| from the schema looks like this:</p><p><codeblock><?xml version="1.0" encoding="UTF-8"?> | |
| <MyAddress xmlns="http://www.ibm.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.ibm.com NewXMLSchema.xsd"> | |
| <name>name</name> | |
| </MyAddress> </codeblock> </p></section> | |
| </refbody> | |
| </reference><?Pub Caret?> | |
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