Good questions.
1. What is RSS? Generally speaking RSS/Atom is set of competing XML formats for representing periodically updated resources on the web; things like weblogs, news sites, forums, bug reports, wiki changes, auction bids,
podcasts, etc.
2. What is an ATOM Feed? Still speaking generally, an RSS/Atom feed is an XML file available at a fixed URL on the web and updated periodically. To monitor a feed, you simply poll the URL.
A feed has some metadata (title, icon, update-time, etc.) and contains entries (also known as items) where an entry is essentially a timestamped chunk of data with some metadata (title, author, update time, publish time, category, etc.).
3. What is the difference between the two technologies? Unfortunately, there are not just two technologies. There are two distinct forks of RSS: the "simple" fork (0.92, 0.93, 2.0, etc.) and the RDF fork (1.0) -- all in all about 10 differerent incompatible versions of RSS. All of the RSS specs are fairly loose and as a result, open to differernt interpretations. Items in an RSS feed typically carry escaped HTML, but each entry can also have an attachment -- i.e. a podcast.
Then there's Atom, the Internet Engineering Task Force (IETF) standard syndication format. IETF is the same standards group the governs specs like HTTP, SMTP and IRC -- as a result the spec (RFC-4287) is well-written, carefully worded and very tight.
Atom is a little differernt from RSS because 1) it requires each entry to have a unique ID and 2) it requires feed publishers to precisely specify the type of content in each entry. An entry's <content> element can carry text, escaped HTML, XHTML or any MIME content-type (incuding binary data) -- so an entry can really carry any type of data. Because of these (and other) things, Atom is much more friendly to developers and for applications other than blogging (i.e. feeds that carry data other than escaped HTML).
4. What is your book all about? The book explores use cases for blogging and feed technology, explains blogs and wiki servers, covers RSS and Atom formats in depth and explains how to use standard web services (XML-RPC based MetaWeblog API and the Atom protocol) to publish to the web. You'll learn how to parse, generate and serve feeds. Examples are in
Java and C#.