Knowledge and reasoning

Vocabulário

English	Significado
propositional logic	Logic combining statements with truth values using logical connectives.
inference/ˈɪnfərəns/	Deriving conclusions from premises using a reasoning rule or model.
forward chaining	Applying rules to known facts to derive additional conclusions.
backward chaining	Starting with a goal and working backward to facts or subgoals that could support it.

English

Rules and consequences

Propositional logic: facts and rules ($P \to Q$); inference applies modus ponens. Forward chaining floods from the facts; backward chaining aims from the query — symbolic reasoning draws conclusions the data never saw.

{exercise:uni-cs1302-rules}

Prática

Forward chaining starts from —

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English

F1 Storm; F2 Weekend; R1 Storm → Delayed; R2 Weekend → HeavyTraffic; R3 HeavyTraffic → Delayed; R4 Delayed → RefundRisk. Forward chaining: wave one derives Delayed and HeavyTraffic, wave two RefundRisk.
Backward chain for RefundRisk: goal ← Delayed (R4) ← Storm (R1) ← fact: proved in three steps, R2/R3 never fire — goal-directed search.

{exercise:uni-cs1302-kb}

Prática

The course KB derives RefundRisk in — waves

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English

Every step is modus ponens on assumed rules, so derivations cannot invent falsehood; completeness (every consequence reachable) is the harder property.
To prove $Q$ by refutation: assume $\neg Q$, derive the empty clause by resolution — the machinery behind SAT solvers. The converse error ($P \to Q$ read as $Q \to P$) is the classic trap.

{exercise:uni-cs1302-sound}

Prática

Modus ponens makes inference —

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