RDF and walled gardens
It seems to me a natural consequence of the increasing bridging of traditional data sources into RDF is that the number of "walled gardens" of RDF is increasing. Walled gardens are areas from which there is no escape, and while they certainly have their uses (in particular controlling who can access what), they erode the overall usefulness of the system as a whole, by meaning that you literally can't get to there from here.
Examples of RDF walled gardens include the FOAF generated by such systems as tribe.net and livejournal. While it is useful that these sites are exposing data in a machine readable web 2.0 format such as RDF/FOAF, the inability to link to people, resources and interests outside the walled garden represent a significant barrier to interoperability. I am the same person in my blog RSS feed, my flickr photo feed, my del.icio.us feed , my tribe FOAF and my hand-edited FOAF, but only the last can I link to the others, despite the fact that they are all in the same format.
How do you overcome a garden walls and fragmented RDF? Well ideally you create a semantic map from each of the gardens into a more widely used frame of reference, but creating and maintaining such mappings is a huge burden in terms of time and energy, particularly for those of us who have data in a dozens (or even hundreds) of walled gardens.
A lighter-weight approach might be to create a service which allows users to associate URIs for "landmark" real-world entities across different walled gardens. Such a service would not map all entities, only relatively small numbers that a user actually cares about, which actually turn out to be important starting seed points for mapping ontologies (an altogether larger and more complex task, but one which might usefully be aided by the presence of existing seeds).
Landmarks for me might be myself (obviously), key people I work with, communities I am involved with and passtimes that interest me.
Such a service would not have to make a big priority of security, because the walled gardens, by their nature, are secure. Simple user authentication might be required to avoid rampant spamming, but would have to be very lightweight, to avoid the service becoming a kind of walled garden itself, with the unauthenticated being able to look in, but not plant seeds of their own. Lightweight authentication would also solve the uniqueness problem (my idea of the key URIs for "open source" my differ from yours), by labelling associations by user.
Hi Stuart -
A nice post, and we've noticed it in the SIOC community as it is one of our prime objectives. We're trying to link discussions across forum types: blogs, BBs, mailing lists. Also, there is the question you mentioned of how do you link accounts across sites. It's not just accounts though, but distributed channels and threads...
Also, we have a Drupal plugin for SIOC metadata which you may be interested in trying out here...
More info at http://rdfs.org/sioc
One simple way I was thinking of linking across these walled gardens would be to just use bidirectional links; link to another profile (via a sioc:User or foaf:OnlineAccount) in your BB signature or blog description, and to do the same on the other site... e.g. on site 1:
foaf:holdsAccount http://url_of_sioc_user_1
and on site 2 the reverse. Or you could claim accounts from your FOAF profile, and make sure there's a reverse link from the accounts themselves (when the inverse of holdsAccount appears!).
I also produce FOAF data from a number of bulletin board sites, but thought too of how can you link it to other RDF - so I would just add a custom user field where people can add their own seeAlso's or whatever to link up to other stuff...
J.