Over on R3's blog they have published a piece of mine called Identity is an Edge Protocol from which I steal this snippet:
"Identity is an edge protocol, and not a nodal protocol. What is valuable is not the node but the relationships that we can examine and record between any two given nodes. It helps to think of the node - the person - as a blank circle, and then imagine in your mind's eye tracing the relationships between the circles."
For the rest, check the post !