Inference Engine
These are the basic "control mechanism" that does actual problem resolving on the basis of rule bases saved in the knowledge of systems base. Further, based on the problem necessity, inference engine invoke a rule base in between the bunch of available rule bases. Whether, its control mechanism is remained separate from the knowledge base, so this can be utilized to evaluate more than one knowledge base at a time.
Interpreter
This acts as a communicating medium in between the inference engine and users.