The authors of "Capability-based Financial Instruments" [1] say that:

"The sociologist Mark Granovetter originally developed [Granovetter
diagrams] to illustrate how the topology of interpersonal relationships
changes over time, as people introduce people they know to each other
[Granovetter73]. Though Granovetter devised this diagram in the context of
human relations, we have found it to be a powerful notation for
understanding the relations between computational objects in a network."

I'm not a sociologist, so I'm going to take it on faith.

Unlike the Giant Presence Services where everybody knows and trusts The
Service and The Service knows everybody, capabilities [2] are a model for
network communication that is much more like the everyday social
interactions we are used to. Capabilities even use similar terminology:
They say that one object may "introduce" other objects that it "knows".
They say that "only connectivity begets connectivity", meaning that you
cannot communicate with an object unless you are introduced to it.

In systems based on global names, once someone knows your name you can't
really prevent them from contacting you. Spam is an example of this
problem: Once a spammer has your email address (which is a kind of name)
they can deluge you with unwanted mail. You can filter it out, but by that
time you've already paid for it. You can escape spam by changing your
address, but this will frustrate people who you *want* to communicate
with. Capabilities solve this problem with "facets", which are special
references that con be revoked without disturbing other communication
paths.

The Giant Presence Services want each person to have a single,
unique name, even though different people want to use
different names for the same person. (For example, many people
simply think of me as "Wes", but someone who knows two people
named Wes is likely to call me "Wes Felter".) Capabilities also have a
solution for this problem called pet names [3].

In summary, I think capabilities are a communication architecture that
promotes privacy and independence instead of subjugation.

[1] http://www.erights.org/elib/capability/ode/index.html
[2] http://www.erights.org/elib/capability/index.html
[3] http://www.erights.org/elib/capability/pnml.html

Wesley Felter - wesley@... - http://felter.org/wesley/