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<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>&lt;acct:customer xmlns:acct="http://www.my.com/acct-REV10">
	&lt;acct:name>Corporation&lt;/acct:name>
	&lt;acct:order acct:ref="5566"/>
	&lt;acct:status>invoice&lt;/acct:status>
&lt;/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>&lt;ful:customer xmlns:ful="http://www.your.com/ful">
	&lt;ful:name>Corporation&lt;/ful:name>
	&lt;ful:order ful:ref="A98756"/>
	&lt;ful:status>shipped&lt;/ful:status>
 &lt;/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>&lt;acct:customer xmlns="http://www.my.com/acct-REV10" xmlns:acct="http://www.my.com/acct-REV10 ">
&lt;name>Corporation&lt;/name>
&lt;order acct:ref="5566"/>
&lt;status>invoice&lt;/status>
&lt;/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>&lt;?xml version="1.0"?>
&lt;schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns:TestSchema="http://www.ibm.com">
 &lt;simpleType name="ZipCodeType">
 &lt;restriction base="integer">
  &lt;minInclusive value="10000"/>
 &lt;maxInclusive value="99999"/>
&lt;/restriction>
 &lt;/simpleType> 
 &lt;!--element definitions skipped -->  
&lt;/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>&lt;?xml version="1.0"?>
&lt;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">
&lt;x:address>
 &lt;x:street>x:Vangerowstrasse&lt;/x:street>
  &lt;x:zipCode>69115&lt;/x:zipCode>
 &lt;x:city>x:Heidelberg&lt;/x:city>
 &lt;/x:address>
    &lt;x:address> 
&lt;x:street>x:Bernal Road&lt;/x:street> 
&lt;x:zipCode>90375&lt;/x:zipCode>
     &lt;x:city>x:San Jose&lt;/x:city>
 &lt;/x:address>
&lt;/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>&lt;?xml version="1.0"?>
&lt;schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns:x="http://www.ibm.com">
&lt;complexType name="AddressType">
&lt;sequence>
&lt;element name="name" type="string">&lt;/element>
&lt;/sequence>
&lt;/complexType>
&lt;element name="MyAddress" type="x:AddressType">&lt;/element>
&lt;/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>&lt;?xml version="1.0"?>
&lt;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 ">
&lt;name>Peter Smith&lt;/name>
&lt;/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>&lt;?xml version="1.0"?>
&lt;schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns:x="http://www.ibm.com" elementFormDefault="qualified">
&lt;complexType name="AddressType">
&lt;sequence>
&lt;element name="name" type="string">&lt;/element>
&lt;/sequence>
&lt;/complexType>
&lt;element name="MyAddress" type="x:AddressType">&lt;/element>
 &lt;/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>&lt;?xml version="1.0"?>
  &lt;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 "> 
&lt;x:name>Peter Smith&lt;/x:name>
 &lt;/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>&lt;?xml version="1.0"?>
&lt;xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns:x="http://www.ibm.com">
&lt;xsd:complexType name="AddressType">
&lt;xsd:sequence>
		 &lt;xsd:element name="name" type="xsd:string">&lt;/xsd:element>
&lt;/xsd:sequence>
 &lt;/xsd:complexType>
 &lt;xsd:element name="MyAddress" type="x:AddressType">&lt;/xsd:element>
&lt;/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>&lt;?xml version="1.0"?>
 &lt;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 ">
&lt;name>Peter Smith&lt;/name>
 &lt;/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>&lt;?xml version="1.0"?>
&lt;xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
&lt;xsd:complexType name="AddressType">
&lt;xsd:sequence>
&lt;xsd:element name="name" type="xsd:string">&lt;/xsd:element>
&lt;xsd:element name="name" type="xsd:string">&lt;/xsd:element>
&lt;xsd:element name="name" type="xsd:string">&lt;/xsd:element> 
&lt;/xsd:sequence> 
&lt;/xsd:complexType>
&lt;xsd:element name="MyAddress" type="AddressType">&lt;/xsd:element> 
&lt;/xsd:schema> </codeblock></p><p>A valid XML instance document
created from the schema looks like this. All elements are unqualified.</p><p><codeblock>&lt;?xml version="1.0"?>
&lt;MyAddress xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="x.xsd">
&lt;name>name&lt;/name>
&lt;/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>&lt;?xml version="1.0"?>
 &lt;xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.ibm.com" xmlns="http://www.ibm.com">
&lt;xsd:complexType name="AddressType">
&lt;xsd:sequence>
&lt;xsd:element name="name" type="xsd:string">&lt;/xsd:element>
&lt;/xsd:sequence>
&lt;/xsd:complexType>
 &lt;xsd:element name="MyAddress" type="AddressType">&lt;/xsd:element>
 &lt;/xsd:schema> </codeblock> </p><p>A valid XML instance document
created from the schema looks like this:</p><p><codeblock>&lt;?xml version="1.0" encoding="UTF-8"?>
&lt;MyAddress xmlns="http://www.ibm.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.ibm.com NewXMLSchema.xsd">
&lt;name>name&lt;/name>
 &lt;/MyAddress>  </codeblock> </p></section>
</refbody>
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