Hi Gordon,

> I am using VisioEA 2003 and am attempting to define a
> frequency constraint
> on a unary predicate.
> I want to specify exactly one. When I leave the minimum at
> 1, and change
> the maximum from 2 to 1,
> the system dims out the 'OK' button and I am unable to define that
> particular frequency constraint.

That is because if every instance of a given object is supposed to
participate in a role and can participate in that role at most one time,
then those constraints are handled by mandatory and uniqueness respectively.

For unary predicates, the UC on the role is implied, so the at most one part
is intrinsically handled.

Further, since unary predicates are binary (i.e. Boolean), the absence of an
object in the role is presumed to be the false condition thereby you know
the population status (it is or it isn't) for every object instance.

If you want every object to always participate in a unary predicate, then it
is constant, and as such not handled by ORM predicates.

As an FYI, I recently wrote a quick bit about frequency constraints here:
http://objectrolemodeling.com/posts/239.aspx.

Hope that helps,
Scot.
..........................
Scot Becker

Orthogonal Software
www.orthogonalsoftware.com