Hi Zille,
it depends on the specific example. For instance if you match two nodes a:A and b:B both with <<preserve*>> and then draw a link between them with <<create*>> it will create for every pair of a's and b' such a link. In this case, it is indeed the Cartesian product.
In general it is like this: the multi-rule is applied for every found match. If you have a rule with a single node of action <<create*>> (and nothing else) in the underlying model you have an empty LHS. There is exactly one match for this LHS, i.e. the empty match. Therefore, I would expect that the application of this rule will create exactly one object (though I have not tested it).
Hope this helps.
Cheers,
Christian
