What Is Extension XML?
There may be times when the feed you subscribe to uses elements that are not part of one of the feed formats. Extension XML extends the specifications to support application-specific data or objects, similar to a plug-in system for feeds. Extension XML refers to a collection of elements outside of the feed format, also known as namespace. Each namespace is identified by a unique URL. Namespace URLs are defined at the beginning of a feed, and are often associated with an easier to remember string. This string is known as a namespace prefix.
For example, a feed that has bank account information might use a bank namespace identified by the URL http://www.example.com/bank, and a namespace prefix of bank. This namespace might have elements such as owner, address, checking and savings. An entry using this namespace would look like the one in Listing 1-3.
Listing 1-3 An Atom extension XML example
<feed xmlns="http://www.w3.org/2005/Atom" |
xmlns:bank="http://www.example.com/bank"> |
... |
<item> |
<title>Account2004</title> |
<bank:owner>John Doe</bank:owner> |
<bank:address>1 Infinite Loop, Cupertino, CA 95014</bank:address> |
<bank:checking>111829384</bank:checking> |
<bank:savings>949289291</bank:savings> |
</item> |
There are many additional namespaces already defined. One of the most popular ones if for an iTunes podcast. A good resource for finding namespaces is The Dublin Core Metadata Initiative, as well as rss-extensions.org.
Understanding the structure and workflow of a feed is important to using the Publication Subscription framework. Knowing about the components of a feed and the organization of the four major feed standards will help you understand the organization of the Publication Subscription framework and its components.
Last updated: 2007-05-11
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