Recognizing levels of interaction is one step. But human relationships are not so one-dimensional. Guy I work with, person from Bible group, AA sponsor, girl I snogged once, sister I send cards to once a year but avoid otherwise because we disagree strongly over politics, boss I trust implicitly but don't want to show my off-hour shenanigans to, et cetera, et cetera, et cetera.<p>Any system which adequately models real relationships will be too complex for usability and any system which is simple enough to have decent usability will only approximate real relationships.