Programming Jabber

Namespace Usage

Chapter 5 frequently referred to namespaces. Jabber’s namespaces are used within the message elements to qualify payloads (distinct content) within these elements. For example:

RECV: <iq id='roster_0' type='result' from='dj@yak/Work'>
        <query xmlns='jabber:iq:roster'>
          <item jid='sabine@yak' name='sabine' subscription='both'>
            <group>Family</group>
          </item>
        </query>
      </iq>

Here the jabber:iq:roster namespace is used to qualify a chunk of XML that contains roster information embedded in an <iq/> element. A payload exists as a subelement of the main element (that is, a child tag of the parent <message/>, <presence/>, or <iq/> tag) and, in XML terms, belongs to a different namespace than the main element.

The namespace of the main elements in the XML document that is streamed across the connection—<message/>, <presence/>, and <iq/> and indeed their “standard” subelements, such as <message/>’s <subject/> tag—is defined in the root tag of the XML document and in this case is jabber:client. Namespaces like jabber:client that are used to qualify such XML document body fragments are described in Section 5.3.2 in Chapter 5. While the main elements in our client connection are qualified by jabber:client, each distinct payload (“attachment” is also a good way to think of these additional chunks of XML) is qualified by one of the specific namespaces listed in this chapter.

Standard Jabber namespaces begin jabber:, with a few exceptions. It could be argued that the exceptions ...