Xml - Namespace (xmlns)

About

namespace in XML 1) are used to be able to have the same node name but in different namespace.

Example

A simple example would be to consider an XML document that contained references to:

  • a customer
  • and an ordered product.

Both the customer element and the product element could have a child element named id (for identifier).

References to the id element would therefore be ambiguous; placing them in different namespaces would remove the ambiguity.

<xml xmlns:c="https://domain.com/customer" xmlns:p="https://domain.com/product">
   <c:id>The customer id</c:id>
   <p:id>The product id</p:id>
</xml>

Usage

XML namespaces are used mainly for providing uniquely named elements and attributes in an XML document.

For a schema vocabulary, the XML namespace provides a naming context for:

  • named type definitions,
  • named model groups,
  • global element declarations
  • and global attribute declarations

The namespace mechanism defines custom namespaces in which the non-standard elements and attributes are supported.

Syntax

A namespace name is a uniform resource identifier (URI) and is declared using the reserved XML pseudo-attribute:

  • xmlns: to define the default namespace
  • or xmlns:name: to define a namespace where name is the unique namespace identifier (called also a prefix).

For example, the following JSF tag library declaration maps the h prefix to the http://java.sun.com/jsf/html namespace uri.

<xml xmlns:h="http://java.sun.com/jsf/html" >

http://java.sun.com/jsf/html doesn't represent a web page, it's just an unique identifier

Default

The default namespace of a document is defined without the name.

Example for an XHTML document

<html xmlns="http://www.w3.org/1999/xhtml">

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