| <?xml version="1.0" encoding="UTF-8"?> | |
| <!--Arbortext, Inc., 1988-2008, v.4002--> | |
| <!DOCTYPE reference PUBLIC "-//OASIS//DTD DITA Reference//EN" | |
| "reference.dtd"> | |
| <?Pub Sty _display FontColor="red"?> | |
| <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?> | |
| <?Pub *0000012038?> |