1 / 9

Using Definite Knowledge

Using Definite Knowledge. Notes for Ch.3 of Poole et al. CSCE 580 Marco Valtorta. Definite Clause Language. A database language A question-answering system A programming language A representation and reasoning systems (RRS). Definite Clauses as RRS.

gwynethj
Download Presentation

Using Definite Knowledge

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Using Definite Knowledge Notes for Ch.3 of Poole et al. CSCE 580 Marco Valtorta

  2. Definite Clause Language • A database language • A question-answering system • A programming language • A representation and reasoning systems (RRS)

  3. Definite Clauses as RRS • Which concepts and individuals to represent? • At what level of detail? • Is each clause true in the intended interpretation? • If so, a sound proof procedure will generate only answers that are true in the intended interpretation! • Do the rules for the predicates cover all cases?

  4. House Wiring (elect.pl) • Review Fig. 3.1 (same as 1.3) • Level of detail (abstraction) influenced by goals of modeling and available information • Determine whether light are on or off • Voltage and frequency are irrelevant • Common-sense level: we may ignore Kirkhoff’s law

  5. Individuals and Relations • Wires, switches, lights, outlets, circuit breakers. • Relationships represented by predicates: • light(L)---L is a light • lit(L)---L, a light, is lit • live(W)---W, a wire, has current • up(S)---S, a switch, is up • down(S) • ok(E)---E, a circuit breaker or a light, is not blown • connected_to(X,Y)---current (if present at Y) would flow to X.

  6. Axiomatize! • Write what is true in the intended interpretation, using constant and predicate names. • Start with facts. • light(l1)---l1 is a light • down(s1)---switch s1 is down • ok(l2)---l2 is not blown • There is a “light” predicate but no “switch” predicate. Why? • Because we distinguish lights when we define “lit” • Because switches cannot be broken

  7. Keep axiomatizing! • Rules, e.g.: • connected_to(w0,w1) <- up(s2) • Is this true in the intended interpretation? Check it! • Check what? The figure! • connected_to(w5, outside). • Should connected_to be transitive? Symmetric? Reflexive? • Maybe, but it is not in elect.pl!

  8. More Rules for House Wiring • lit(L) <- light(L) & ok(L) & live(L). • A recursive definition: • live(Y) <- connected_to(Y,Z) ^ live(Z). • live(outside).

  9. Is this axiomatization good? • Every clause is true in the intended interpretation. • Some “true” facts are not represented at all. • Some are impossible to represent in definite clause logic without introducing new predicates or constants, e.g.: • “If a light is ok and live and it is not lit, then it is blown” requires a negated atom in the body of a clause!

More Related