Jonathan Lang wrote:
In short, R3 isn't neccessarily a subset of A; it's a superset of A &
B. In a partial ordering graph, there's no reliable ordering between
R3 and A.
The standard syntax for creating roles can't reliably produce a subset
of an existing role, because it always allows you to add to it.
Yes, but I was conjecturing that the additions to A&B are pushed
down to A and B such that their intension sets remain strict supersets
The only problem that might crop up is the use of 'A | B' in
signatures to mean 'can match any of A, B' - that is: in signatures,
'A | B' refers to the junctive operator; while in the above proposal,
'A | B' refers to the set union operator. Different semantics.
In fact if we decide to specify a role combination syntax then it
should be the same everywhere. That means in a signature A|B would
require a more specific type and pure A or B wouldn't be admissible.
To get the old meaning of | you have to write A&B or perhaps the
juxtaposition which currently means what A|B should mean. Alternatively
the meaning of the role combination A&B could be defined to mean the
union and A|B the intersection.