With all of the euphoria surrounding the recently announced "convergence" between OpenID and Cardspace, I thought this would be a good time to revisit a taxonomy I created two years ago. Although I did not intend to be controversial, I drew some of flack for assigning LID the role of a unicycle in my taxonomy.
Now two years later, LID has become a subset of YADIS, YADIS has merged with OpenID, and OpenID will be supported within Cardspace nee Infocards. (Also, Liberty and SAML became one.) Where does this evolution leave the transportation taxonomy?
Cardspace had not yet been announced at the time I posted my original taxonomy. When it was announced as Infocards I worried that it might become the Segway of identity (my worry was based on the inner circle hype that accompanied its rumored existence.) Thankfully, Cardspace has developed, under Kim's guidance, into the motor vehicle of identity - I am placing it into my taxonomy as the Pickup Truck. The Pickup Truck is versatile, it is useful for both work and entertainment and it is fairly straightforward to operate for the average driver. These are all characteristics that map pretty neatly to the form and function Cardspace provides in the identity world.
As for the "convergence" between OpenID and Cardspace, I still view OpenID as a Unicycle relative to other methods of porting identity across security domains. Unicycles are fun and for a small subset of transportation needs they serve a well defined purpose. Such as riding around in your driveway juggling oranges...but if I put a Unicycle in the back of a Pickup Truck when I go to the grocery store to buy those oranges, does that represent convergence between the Unicycle and the Pickup Truck? Does that give the Unicycle a role in the grocery hauling task? I say no. Similarly, OpenId will play a limited role in making identities portable - primarily for fun stuff. Whether on its own or as part of Cardspace, OpenID will remain use limited.
Despite what some in the OpenID community would believe, the Unicycle is not all that pejorative a metaphor and the taxonomy is not a hierarchy. I originally created it as a fun way to classify identity systems and to better organize the conversation around where different approaches to portable identity best fit and I think it still serves that purpose.
Also, as a longtime employee of the only company that has developed code supporting all three versions of SAML, WS-Federation, SPML, Cardspace, and OpenID, I have no vested interest in taking sides. In fact, Vive le difference! Vive le Pickup Truck! and long live the Unicycle too.