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).
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.