Group membership and OpenID

Martin Atkins has posted a note about the Group Membership Protocol to the OpenID mailing list.

[the] Group Membership Protocol is a very simple means by which a group of URIs (which are probably OpenID identifiers, but don't necessarily need to be) can be enumerated and queried.

This looks very interesting.  A simple idea but one that appears to have lots of applications - many of which will lie outside the identity management area, possibly including those that currently fall under the 'collection description' umbrella.  It'll be interesting how it develops.

I'm adding it to my wish list for Second Life, Facebook and Twitter.  Mind you... all of those services also need to support OpenID!