Learn Xml: CODING3

<body>

<books>

<book>

<title>XSLT Programmers Reference</title>

<author>Michael Kay</author>

</book>

</books>

</body>

</html>

In this example, there’s no way to distinguish between the two title elements even though they are

semantically different. A namespace can solve this problem by providing a unique identifier for a

collection of elements and/or attributes. This is accomplished by prefixing each member element and

attribute with a name, uniquely identifying them as part of that namespace. Grouping elements into a

namespace allows them to be referenced easily by many XML documents and allows one XML document

to reference many namespaces. XML namespaces are a form of qualifying attribute and element names.

This is done within XML documents by associating them with namespaces that are identified with

Universal Resource Indicators (URIs).

A URI is a unique name recognized by the processing application that identifies a particular resource.

URIs includes Uniform Resource Locators (URL) and Uniform Resource Numbers (URN).

The following is an example of using a namespace declaration that associates the namespace

http://www.w3.org/1999/xhtml with the HTML element.

The xmlns keyword is a special kind of attribute that indicates you are about to declare an XML

namespace. The information between the quotes is the URI, pointing to the actual namespace — in this

case, a schema. The URI is a formal way to differentiate between namespaces; it doesn’t necessarily need

to point to anything at all. The URI is used only to demarcate elements and attributes uniquely. The

xmlns declaration is placed inside the element tag using the namespace.

Namespaces can confuse XML novices because the namespace names are URIs and therefore often

mistaken for a Web address that points to some resource; however, XML namespace names are URLs that

don’t necessarily have to point to anything. For example, if you visit the XSLT namespace (http://www

.w3.org/1999/XSL/Transform), you would find a single sentence: “This is an XML Namespace

defined in the XSL Transformations (XSLT) Version 1.0 specification.” The unique identifier is meant to

be symbolic; therefore, there’s no need for a document to be defined. URLs were selected for namespace

names because they contain domain names that can work globally across the Internet and they are unique.

The following code shows the use of namespaces to resolve the name conflict in the preceding example.

<head>

</head>

<body>

<book>

<title>XSLT Programmers Reference</title>

<author>Michael Kay</author>

</book>

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