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Forward vs backward chaining

Short answer

Forward chaining is data-driven, starting from facts and firing rules to reach a goal, possibly deriving irrelevant facts. Backward chaining is goal-driven, starting from the goal and working backward to find supporting facts; it is focused but may loop.

Differentiate between forward chaining and backward chaining.

Both are inference methods for rule-based systems with IF-THEN rules.

BasisForward chainingBackward chaining
DirectionFrom known facts towards the goal (bottom-up)From the goal back to facts (top-down)
ApproachData-driven: fires rules whose conditions are satisfied, adding new factsGoal-driven: finds rules whose conclusion matches the goal and tries to prove their conditions as sub-goals
StartFacts / initial dataHypothesis / goal to prove
StrategyBreadth-first likeDepth-first like
EfficiencyMay derive many irrelevant factsFocuses only on rules relevant to the goal
Best forMonitoring, planning, design, interpretation (many conclusions from data)Diagnosis, answering a specific query (few goals)
Example systemsOPS5, XCONMYCIN, Prolog
TerminationStops when no new facts or goal is derivedStops when the goal is proved or no rules remain

✓ Answer checked by Claude Opus 5.5 (high effort)

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