XML Namespaces

• Defined in the XML namespaces recommendation
• An XML namespace is a collection of names, identified by a URI reference (RFC2396), which are used in XML documents as element types and attribute names.
• You use them when you need to use more than one DTD or Schema.
• A namespace is declared as using the xmlns attribute:

<x xmlns="http://www.w3.org/TR/REC-html40"
   xmlns:edi="http://ecommerce.org/schema">
  <!-- the "edi" prefix is bound to http://ecommerce.org/schema
       for the "x" element and contents -->
   <edi:price units="Euro">32</edi:price>
   <lineItem edi:taxClass="exempt">Baby food</lineItem>
</x>

• The edi is called the namespace prefix.
• After this declaration and within the x element any tag tagname that is appears as edi:tagname will be considered part of the edi schema.
• If the prefix is missing then that namespace becomes the default namespace.
• Namespace scopes are nested:

<?xml version="1.0"?>
<!-- initially, the default namespace is "books" -->
<book xmlns="urn:loc.gov:books"
      xmlns:isbn="urn:ISBN:0-395-36341-6">
  <title>Cheaper by the Dozen</title>
  <isbn:number>1568491379</isbn:number>
  <notes>
    <!-- make HTML the default namespace for some commentary -->
    <p xmlns="urn:w3-org-ns:HTML">
      This is a <i>funny</i> book!
    </p>
  </notes>
</book>