Groups vs. Roles

There was some discussion at the F2F regarding if groups and roles are the
same thing. Here is my take. I know that others may also have some
illuminating remarks.

The following seem to be the case:

For all roles R, there exists a group G such that all members M of G have
role R.

It is not true that for all groups G, there exists a role R such that all
members M of G have role R. For example, the group of workers in the US may
have a certain set of privileges based on their group. However, they won't
all have the same role.

If my memory serves me correctly the equivocation of expressions of the same
form as the two above is such a common error in formal logic that it
actually has a name. Of course, I can't remember it ...


Simon Y. Blackwell 
CTO 
Psoom, Inc. 
Voice & Fax: 415-762-9787 

P.S. Bill, I would have expressed the above in predicate calculus, but I
didn't want you to tune out ... actually, I'm way too rusty to get it right!
Anyone else care to give it a try Pierangela? ;-)