I too would like to hear about getting facts from an sql db, and writing back results from prolog - it's hard to see how a prolog text file can/could be used as a source for transactional problems like booking (making sure the answer you find can be committed while still valid).

I suppose one could have a prolog service that came up with suggestions, ordered by preference, and then attempt committing them in order to the actual transactional storage layer. But I don't see how you could avoid re-implementing transactions.

With an rdms you could look for options, and attempt a booking in a transaction, and have a fairly established way to resolve conflicts.