Not to disappoint you, but I haven't considered prolog for this task, as the entire system is written in perl.
What this means that it gives us an opportunity to mimic prolog/logical programming via perl modules and operator overloading.

First we list some "Truths" about our world, then we attempt to derive the truthfulness of other relationships, based on the principals of logical reasoning.
I defintely liked your verbal derivation of the problem. What I have mentioned is just a simple ranking problem. Your idea could be applied in general and we can prepare a complex data set to come up with the complicated query.
More pointers in this direction, if you have done some research, would be definitely helpful.