These are my notes on the Build Contentcentric Applications on RSS, Atom, and the Atom API session by Ben Hammersley.
This was a 3.5 hour tutorial session [which actually only lasted 2.5 hours].
At the beginning, Ben was warned the audience that the Atom family of specifications are still being worked on but should begin to enter the finalization stages this month. The specs have been stable for about the last 6 months, however anything based on work older than that (e.g. anything based on the Atom 0.3 syndication format spec) may be significantly outdated.
He indicated that there were many versions of syndication formats named RSS, mainly due to acrimony and politics in the online syndication space. However there are basically 3 major flavors of syndication formats; RSS 2.0, RSS 1.0 and Atom.
One thing that sets Atom apart from the other formats is that a number of optional items from RSS 1.0 and RSS 2.0 are mandatory in Atom. For example, in RSS 2.0 an item can contain only a <description> and be considered valid while in RSS 2.0 an item with a blank title and a RDF:about (i.e. link) can be considered valid. This is a big problem for consumers of feeds, when basic information like the date of the item isn’t guaranteed to show up.
There then was a slide attempting to show when to use each syndication format. Ben contended that RSS 2.0 is good for machine readable lists but not useful for much else outside of displaying information in an aggregator. RSS 1.0 is useful for complex data mining, not useful for small ad-hoc web feeds. Atom is best of both worlds, a simple format yet strictly defined data.
I was skeptical of this definition especially since the fact that people are using RSS 2.0 for podcasting flies in the face of his contentions about what RSS 2.0 is good for. In talking with some members of the IE team, who attended the talk with me, about this part of the talk later they agreed that Ben didn’t present any good examples of use cases that the Atom syndication format satisfied that RSS 2.0 didn’t.
Atom has a feed document and an entry document, the latter being a new concept in syndication. Atom also has a reusable syntax for generic constructs (person, link, text, etc). At this point Marc Canter raised the point that there weren’t constructs in Atom for certain popular kinds of data on the Web. Some example Marc gave were that there are no explicit constructs handle tags (i.e. folksonomy tags) or digitial media. Ben responded that the former could be represented with category elements while the latter could be binary payloads that were either included inline or linked from an entry in the feed.
Trying a different tack, I asked how one represented the metadata for digital content within an entry. For example, I asked about doing album reviews in Atom. How would I provide the metadata for my album review (name, title, review content, album rating) as well as the metadata for the album I was reviewing (artist, album, URL, music sample(s), etc) and his response was that I should use RSS 1.0 since it was more oriented to resources talking about other resources.
The next part of the talk was about the Atom API which is now called the Atom publishing protocol. He gave a brief history of weblog APIs starting with the Blogger API and ending with the MetaWeblog API. He stated that XML-RPC is inelegant while SOAP is “horrible overkill” for solving the problem of posting to a weblog from an API. On the other hand REST is elegant. The core principles of REST are using the HTTP verbs like GET, PUT, POST and DELETE to manipulate representations of resources. In the case of Atom, these representations are Atom entry and feed documents. There are four main URI endpoints; the PostUri, EditUri, FeedUri, and the ResourcePostUri. In a technique reminiscent of RSD, websites that support Atom can place pointers to the API end points by using <link> tags with appropriate values for the rel attribute.
At the end of the talk I asked what the story was for versioning both the Atom syndication format and the publishing protocol. Ben floundered somewhat in answering this question but eventually pointed to the version attribute in an Atom feed. I asked how would an application tell from the version attribute if it had encountered a newer but backwards compatible version of the spec or was the intention that clients should only be coded against one version of Atom? His response was that I was ‘looking for a technological solution to social problem’ and more importantly there was little chance that the Atom specifications would change anyway.
During the break, Marc Canter and I talked about the fact that both the Atom syndication format and Atom publishing protocol are simply not rich enough to support existing blogging tools let alone future advances in blogging technologies. For example, in MSN Spaces we already have data types such as music lists and photo albums which don’t fit in the traditional blog entry syndication paradigm that Atom is based upon. More importantly it is unclear how one would even extend to do this in an acceptable way. Similar issues exist with the API. The API already has less functionality existing APIs such as the MetaWeblog API. It is unclear how one would perform the basic act of querying one’s blog for a list of categories to populate the drop down list used by a rich client which is a commonly used feature by such tools. Let alone, doing things like managing one’s music list or photo album which is what I’d eventually like us to do in MSN Spaces.
The conclusion that Marc and I drew was that just to support existing concepts in popular blogging tools, both the Atom syndication format and the Atom API would need to be extended.
There was a break, after which there was a code sample walkthrough which I zoned out on.