Expert Systems Questions and Answers

Answer: A

Data-driven inference pursues every consequence of the facts, so in a large base most of the work has nothing to do with the question of interest. Redundant questioning and repeated subgoals are backward-chaining faults, and duplicated knowledge bases belong to nothing here. Goal-directed filtering, or a hybrid regime, is the usual remedy when a forward system must answer specific queries. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: B

A subgoal needed by several rules is proved afresh each time unless the engine caches results, which is why memoisation matters in goal-directed systems. Irrelevant derivation and exhaustive matching are forward-chaining costs, the latter addressed by Rete. Recognising that the two regimes fail in opposite ways is what guides the choice, and hybrid engines exist precisely to get both benefits.

Answer: C

Real systems commonly chain forward from newly supplied data to derive cheap consequences, then chain backward to test the hypotheses that survive. The mixture keeps both the irrelevant derivation and the repeated questioning within bounds. Committing to one direction is a textbook simplification. Knowing that the choice is a spectrum rather than a dichotomy is the practical point.

Answer: D

Explanation is possible precisely because the knowledge is stored as inspectable rules rather than compiled into procedural code, so the sequence of rules that fired can be replayed as a justification. A conventional program has no comparable record. This is the clearest practical dividend of the separation of knowledge from control, and it was decisive in gaining user acceptance for MYCIN and its successors.

Answer: A

Modularity is real at the level of a single rule but breaks down in aggregate, because rules interact through working memory in ways their authors never considered. XCON's history, with thousands of rules and a permanent maintenance team, is the standard counter-example. So the reason is true as stated and the assertion is false, which is exactly the gap that verification tools and model-based methods were developed to close.

Answer: B

The reason states the assumption correctly, and it is that very assumption which makes the assertion false: correlated findings are double counted and confidence is overstated. Heckerman showed certainty factors correspond to probabilities only under conditions real domains violate. The pattern of a true reason establishing the falsity of the assertion is common in this topic and worth reading carefully.

Answer: C

Because the diagnosis is computed from a model of correct behaviour rather than from a catalogue of known faults, any discrepancy can be localised whether or not it was anticipated. That is exactly the brittleness a rule base suffers from. The cost is the effort of building and simulating the model, which is why shallow and deep methods are so often layered together in a single system.

Answer: D

Working memory holds facts specific to the current case and is cleared when the consultation ends, whereas the knowledge base is the system's long-term store and persists. Reversing the two is the standard confusion. The division corresponds to the distinction between what an expert knows and what an expert has just been told, and it is what allows one knowledge base to serve an unlimited number of cases.

Answer: A

Forward chaining begins with the available facts and derives whatever follows, which is the definition of data-driven, while backward chaining begins with a goal and is therefore goal-driven. The pairing of the two labels with the two directions is asked constantly and is worth fixing firmly. Diagnosis chains backward, monitoring chains forward, and most deployed systems mix the two.

Answer: B

A shell is exactly what remains when the domain knowledge is stripped out: the engine, the explanation facility, the working memory and the authoring tools. EMYCIN was created by performing that removal on MYCIN. Supplying the knowledge is the buyer's job, and it is the expensive part. Getting this the right way round is the whole point of the shell concept.