The transformation layer will apply an inference process (similar to forward-chaining) and check for each node in the plan tree to see which query transformations apply to that node.

Inference rules implement forward inferencing, backward chaining, Prolog-style unification or other artificial intelligence (ai) -style rules.

And in fact, when I stepped back and looked at my domain model, I realized that I had essentially written my own forward-chaining rules engine.