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XML Namespaces

XML namespaces are used to avoid name conflicts between XML elements.

Name Conflicts between XML Elements and Resolution​

A conflict could happen when you try to mix XML documents from different XML application.

The following is an example of conflict:

<table>  
	<tr>  
		<td>Milan</td>  
		<td>Rome</td>  
		<td>Venice</td> 
	</tr>  
</table>
<table>  
	<name>PC desk</name>  
	<width>90</width>  
	<length>150</length>  
</table>

Both contain a <table> element but the XML elements have different content and meaning. If they merged together, there would be a name conflict.

To resolve name conflicts we use a name prefix.

For example:

<firstprefix:table>  
	<firstprefix:tr>  
		<firstprefix:td>Milan</firstprefix:td>  
		<firstprefix:td>Rome</firstprefix:td>  
		<firstprefix:td>Venice</firstprefix:td> 
	</firstprefix:tr>  
</firstprefix:table>

<secondprefix:table>  
	<secondprefix:name>PC desk</secondprefix:name>  
	<secondprefix:width>90</secondprefix:width>  
	<secondprefix:length>150</secondprefix:length>  
</secondprefix:table>

In this way, we have resolved the conflict: elements of the first table have firstprefix: prefix while elements of the second table have secondprefix: prefix.

note

Basically, we changed the <tagname> to <prefixname:tagname> with prefixes to resolve conflicts

XML Namespace​

A namespace must be defined in order to use prefixes in XML.

The namespace is defined using an xmlns attribute in the start tag of an element, following this syntax: xmls:prefixname="URI".

<root>

	<firstprefix:table xmlns:firstprefix:tr="http://www.w3.org/TR/html4/">  
		<firstprefix:tr>  
			<firstprefix:td>Milan</firstprefix:td>  
			<firstprefix:td>Rome</firstprefix:td>  
			<firstprefix:td>Venice</firstprefix:td> 
		</firstprefix:tr>  
	</firstprefix:table>

	<secondprefix:table xmlns:secondprefix:name="https://tutorialreference.com/furniture">  
		<secondprefix:name>PC desk</secondprefix:name>  
		<secondprefix:width>90</secondprefix:width>  
		<secondprefix:length>150</secondprefix:length>  
	</secondprefix:table>
	
</root>
note

Namespaces can also be declared in the XML root element

<root xmlns:firstprefix="first-URI" xmlns:secondprefix="second-URI">
	...
</root>
note

The purpose of the URI is to give the namespace a unique name. Also, it isn't used by the parser.

XML Namespace as Default Namespace​

Defining a default namespace avoids the use of prefixes in all descendant elements.

A default namespace is written as xmlns="namespaceURI".

For example:

<table xmlns="http://www.w3.org/TR/html4/">  
	<tr>  
		<td>Milan</td>  
		<td>Rome</td>  
		<td>Venice</td> 
	</tr>  
</table>
<table xmlns="https://tutorialreference.com/furniture">  
	<name>PC desk</name>  
	<width>90</width>  
	<length>150</length>  
</table>

Namespaces and XSLT​

XSLT is a language used to transform XML documents into other formats.

Read our XSLT Tutorial to learn more about XSLT.

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