Robert Scoble wrote

I see over on Evan Williams site that it looks like Google (er, Blogger, which is owned by Google) is going to support Atom. So far Microsoft has been supporting RSS 2.0 (we've spit out RSS 2.0 on MSDN, on the PDC app, on MyWallop, and in a few other places). Atom is a syndication format that's similar, but slightly different from RSS. I wonder how the market will shake out now.

Evan: can you explain, in layman's terms, why you support Atom and not RSS?

This question is misleading. There are two parts to ATOM that are being discussed by Google, the ATOM API and the ATOM syndication format. The ATOM API is competitive with technologies like the Blogger API, MetaWeblog API and the LiveJournal API while the ATOM syndication format competes with technologies like RSS 1.0 and RSS 2.0.

There has been enough written about the history of feed syndication formats named "RSS" so I'll skip that discussion and move directly to discussing the history of weblog posting APIs.

The Blogger API was originally developed by Blogger (now owned by Google) as a way of allowing client applications to talk to blogger weblogs (using client applications such as w.bloggar). This API was later adopted by other blogging tools such as Radio Userland. However Dave Winer decided he didn't like some of the perceived deficiencies in the Blogger API and forked it thus creating the MetaWeblog API. Later on the Blogger folks came out with version 2.0 of the Blogger API which led to online war of words with Dave Winer because he felt they should use his forked version instead even though his version removed functionality that was crucial to Blogger. Eventually Blogger backed off from implementing v2.0 of thier API and has been waiting for an alternative which presented itself in the ATOM API. Most of this history is available from  Evan Williams's blog post entitled the Tragedy of the API.

<update source="Dave Winer" >

1. ManilaRPC came first, way before all the others you mention. It was an XML-RPC then SOAP-based API for driving Manila, and is still in use today, and is much deeper than any of the other APIs.
2. The MetaWeblog API addressed a very well-known deficiency in the Blogger API, no support for titles. You neglected to mention that it was broadly supported by tools and blogging systems, by everyone except Blogger.

The ATOM effort is aimed at replacing both the popular syndication formats and the popular weblog publishing APIs. Both of which have been burdened with histores full of turbulent turf battles and personal recriminations.  

Based on my experiences working with syndication software as a hobbyist developer for the past year is that the ATOM syndication format does not offer much (if anything) over RSS 2.0 but that the ATOM API looks to be a significant step forward compared to previous attempts at weblog editting/management APIs especially with regard to extensibility, support for modern practices around service oriented architecture, and security. The problem is that if one implements the ATOM API it makes sense that since this API uses the feed syndication format as the payload of the messages sent between the client and the server then one should also implement the ATOM syndication format. This is probably why Blogger/Google will support both the ATOM API and the ATOM syndication format.

I personally tend to agree with Don Park's proposal

IMHO, the most practical path out of this mess is for the Atom initiative to hi-jack RSS 2.0 and build on it without breaking backward compatibility.  A new spec will obviously have to be written to avoid copyright problems with Dave's version of the RSS 2.0 spec, but people were complaining about the old spec anyway.

As to the Atom API, I won't bitch about it any more if RSS 2.0 is adopted as the core Atom feed format because the feed format is far more important than the API.  This should satisfy Evan Williams since his real beef is with the API.  Yes, there are some issues people have with RSS 2.0 but they can be ignored or worked-around with extensions until later, hopefully much later.

This compromise will give the best of all world's to users. There is no discontinuity in syndication formats yet blog editting APIs are improved and brought in line with 21st century practices. I've mentioned this on the atom-syntax mailing list in the past but the  idea seemed to receive a cold reception.

Regardless of what ends up happening, the ATOM API is best poised to be the future of weblog editting APIs. The ATOM syndication format on the other hand...