Chris Ceppi has picked up and extended an interesting piece by Stefan Brands where he uses a transportation analogy to classify personal digital identity systems such as FOAF and LID as bicycles whereas SAML and Liberty are jet planes. Chris goes on to say:
Under this taxonomy, I see LID as a unicycle – novel, but impractical and limited to people with a very specialized set of skills. As has been dissected in numerous other places (most expertly at Burningbird), LID's dependence on URLs as an identifier misses the mark in a number of ways – like a unicycle, LID is just not a useful way to get around.
SXIP would then be a Cessna – complex enough (with its hosted identities and 3rd party assertions) that you need a pilots license to use it, but not rigorous enough for a broad set of air travel requirements (e.g. SXIP is not based on standards).
SAML and Liberty as they have currently been implemented might be considered the space shuttles of identity.
I'm not sure I buy this taxonomy – I think several of the systems have a lot to offer – but it is really amusing. And I do buy Chris’ conclusions – we have work to do in getting to a unifying metasystem.
