Simple List Extensions for RSS 2.0 (Gnomedex)
I’m back from the Gnomedex 5 conference.
The headlines are increasing support from mainstream companies for RSS, including platform support that makes it write RSS enabled applications and extensions to RSS itself that increase the scope of content and media that work well in RSS.
In this post I’d like to consider specifically the extensions to RSS.
Dean Hachamovitch and the Microsoft folks had a proposed RSS extension called Simple List Extensions, licensed under the creative commons license. Simple List Extensions should make things like RSS job feeds, to do lists, and other list based subscriptions work much better over RSS.
The problem is that RSS today is optimized for feeds of individuals posts that accumulate over time. It doesn’t work well for lists whose items can reordered, updated, and deleted– these changes will show up as entirely new posts or not all. And there is now way for a feed to specify additional sorts and filter that would be relevant to the content in that feed.
The simple list extensions allow a RSS feed to be designated as a list, with metadata to describe the relevant sort orders and category filters that might applied. Downlevel clients will ignore the extensions, smart clients will present a richer and better UI based on them.
Amazon had created an RSS feed of their wish lists with these extensions, and Dean demonstrated an aggregator taking advantage of them. He could click on a “books” link to filter the feed items to just books and then “price” to sort by price. The sorting and filterign are very fast because they happened entirely on the client.
The snippet of XML for doing this looks something like the following:
<cf:listinfo>
<aws:DateAdded type=”text”>Date Added <aws:Price type=”number”>Price</aws:Price>
…
</cf:listinfo>
Simple List Extensions points the way towards what is likely to be a number of semantic hints to RSS clients. I don’t worry to much about Simple List Extensions adoption– it solves a very simple problem simply, and has a reasonable Creative Commons license– but I foresee the potential for ferocious and dueling standards over future extensions.
The one down side in all of this is that support for Simple List Extensions seems to be tied up in the slow moving Longhorn bandwagon. If Microsoft is serious about evangelizing the standard they have support for it now, not when Longhorm ships. They don’t even need to ship client bits to do this. If their portal consumes RSS they could extend the portal to understand the list extensions and evangelize them among content author.
If Microsoft doesn’t do this, other companies will. I can easily imagine Yahoo and Google collaborating to define a competing standard for RSS lists and implementing it on their portals, which already support RSS. From the perspective of someone who would like to see the functionality arrive sooner rather than later and achieve wide adoption, a standard that was born in this fashion might be preferable.
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