Clay Shirky has posted a very interesting clarification of his earlier comments about the RELATIONSHIP schema.

Human social calculations are in particular a kind of thing that cannot be made formal or explicit without changing them so fundamentally that the model no longer points to the things it is modeled on...

The flaw in RELATIONSHIP is not that you can?t characterize someone as a colleague and an employee, but rather that you can?t completely specify the fullness of any reasonably complex relationship, you can?t know in advance which of those characterizations you would use in what circumstances, and you can?t make even a subset of those things explicit without changing the thing you are trying to describe. Source

I completely agree with Clay's comment about the importance of circumstance. I have been working on the issue of circumstance in developing a framework for customized social networks. There needs to be a means to contextualize the relationship: friends, co-workers, co-students, acquaintences, strangers (one-way), family members, participants in a common activity, and so on. There may also be more than one context: family members who are also co-workers.

Providing a relationship contexts would place restrictions on the nature of the relationships that could occur between two personae, which would also provide a higher level of expressiveness for users. Further, I believe that working circumstance into a social networking standard would also simplify the development of a means to fetch and query the distributed data.