
an internal constraint to the predicate, press the Add Internal button to invoke the Add
Constraint dialog and add the constraint there. To add an external constraint to the pred-
icate, press the Add External button to invoke the Add Constraint dialog, and add the con-
straint there.
5.5 Set-Comparison Constraints
If two roles are played by the same object type, or their object types share a common
supertype, they are said to be compatible, and it is meaningful to compare their popu-
lations. The same is true for role-sequences (ordered lists of roles). For databases, only
three set-comparison operators are relevant: subset (⊆), equality (=) and mutual ...