Joe Gregorio, one of the editors of RFC 5023: The Atom Publishing Protocol, has declared it a failure in his blog post titled The Atom Publishing Protocol is a failure where he writes
The Atom Publishing Protocol is a failure. Now that I've met by blogging-hyperbole-quotient for the day let's talk about standards, protocols, and technology… AtomPub isn't a failure, but it hasn't seen the level of adoption I had hoped to see at this point in its life. … Thick clients, RIAs, were supposed to be a much larger component of your online life. The cliche at the time was, "you can't run Word in a browser". Well, we know how well that's held up. I expect a similar lifetime for today's equivalent cliche, "you can't do photo editing in a browser". The reality is that more and more functionality is moving into the browser and that takes away one of the driving forces for an editing protocol. … Another motivation was the "Editing on the airplane" scenario. The idea was that you wouldn't always be online and when you were offline you couldn't use your browser. The part of this cliche that wasn't put down by Virgin Atlantic and Edge cards was finished off by Gears and DVCS's. … The last motivation was for a common interchange format. The idea was that with a common format you could build up libraries and make it easy to move information around. The 'problem' in this case is that a better format came along in the interim: JSON. JSON, born of Javascript, born of the browser, is the perfect 'data' interchange format, and here I am distinguishing between 'data' interchange and 'document' interchange. If all you want to do is get data from point A to B then JSON is a much easier format to generate and consume as it maps directly into data structures, as opposed to a document oriented format like Atom, which has to be mapped manually into data structures and that mapping will be different from library to library.
The Atom effort rose up around the set of scenarios related to blogging based applications at the turn of the decade; RSS readers and blog editing tools. The Atom syndication format was supposed to be a boon for RSS readers while the Atom Publishing Protocol was intended to make thing better for blog editing tools. There was also the expectation that the format and protocol were general enough that they would standardize all microcontent syndication and publishing scenarios.
The Atom syndication format has been as successful or perhaps even more successful than originally intended because it's original scenarios are still fairly relevant on today's Web. Reading blogs using feed readers like Google Reader, Outlook and RSS Bandit is still just as relevant today as it was six or seven years ago. Secondly, interesting new ways to consume feeds have sprung in the form of social aggregation via sites such as FriendFeed. Also since the Atom format is actually a generic format for syndicating microcontent, it has proved useful as new classes of microcontent have shown up on the Web such as streams of status updates and social network news feeds. Thanks to the Atom syndication format's extensibility it is being applied to these new scenarios in effective ways via community efforts such as ActivityStrea.ms and OpenSocial.
On the other hand, Joe is right that the Atom Publishing Protocol hasn't fared as well with the times. Today, editing a blog post via a Web-based blog editing tool like the edit box on a site like Blogger is a significantly richer experience than it was at the turn of the century. The addition of features such as automatically saving draft posts has also worked towards obviating some of the claimed benefits of desktop applications for editing blogs. For example, even though I use Windows Live Writer to edit my blog I haven't been able to convince my wife to switch to using it for editing her blog because she finds the Web "edit box" experience to be good enough. The double whammy comes from the fact that although new forms of microcontent have shown up which do encourage the existence of desktop tools (e.g. there are almost a hundred desktop Twitter apps and the list of Facebook desktop applications is growing rapidly), the services which provide these content types have shunned AtomPub and embraced JSON as the way to expose APIs for rich clients to interact with their content. The primary reason for this is that JSON works well as a protocol for both browser based client apps and desktop apps since it is more compatible with object oriented programming models and the browser security model versus an XML-based document-centric data format.
In my opinion, the growth in popularity of object-centric JSON over document-centric XML as the way to expose APIs on the Web has been the real stake in the heart for the Atom Publishing Protocol.
FURTHER READING
JSON vs. XML: Browser Programming Models – Dare Obasanjo on why JSON is more attractive than XML for Web-based mashups due to presenting a friendlier programming model for the browser.
JSON vs. XML: Browser Security Model - Dare Obasanjo on why JSON is more attractive than XML for Web-based mashups due to circumventing some of the browser security constraints placed on XML.
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