2 Logic Paradigm • It focus on what is needed (requirements), instead of how to implement them. It just describe what the problem is and let the computer find a way to solve the problem, instead describing how to solve the problem. • It rely on the environment to find solutions that meet requirements.
3 Predicate Logic • It uses a simplified variation of predicate logic syntax, which is similar to natural language. • Predicate logic eliminate all unnecessary words from sentences, then transform the sentence by placing the relationship (predicate) first and grouping the objects (arguments) after the relationship predicate (object, object, object ....)
4 Natural Language Predicate Logic Type of Predicate A car is fast. fast(car). fact A rose is red. red(rose). fact Bill likes the car if the car is fast. likes(bill, car) :- fast(car). rule Humidity is high if it rains high(humidity):- rains(). rule Jane is mother of Elaine mother_of(jane, elaine). fact Jane is mother of Mike mother_of(jane, mike). fact David is father of Jesse father_of(david, jesse). fact Jesse is father of Obed father_of(jesse, obed). fact Grandmother X of Z if (X is mother of Y and (Y is mother of Z or Y is father of Z) grandmother_of(X, Z) :- mother_of(X, Y), ( mother_of(Y, Z); father_of(Y, Z) ). rule
5 Predicate Logic • Facts: What is known, e.g., Bill likes car and bike, and he travels with one of them likes(bill, car), likes(bill, bike) travels(bill, car); travels(bill, bike) • Rules: What you can infer from the given facts. Rules enable you to infer facts from other facts, e.g., Bill is the father of Joe, if Joe is the son of bill. father(bill, joe) :- son(joe, bill). , means AND ; means OR
8 Install a Prolog Interpreter To enter rules from the command line, type this : [user]. This puts you in a mode where you can enter facts and rules. Otherwise you get this kind of message: ERROR: Undefined procedure: (DWIM could not correct goal) You can then enter facts (or rules) e.g. : father(me,sarah). After having entered the knowledge, type CONTROL-D to come back to the mode where you can enter questions. Then you can ask: ?- father(me,X). X = sarah To quit: halt.
17 Arithmetic Queries ?- X is 3 + 5. X=8 ?- X is 3 mod 2. X=1 ?- X is 3 mod 2 - 1 * 5 / 9. X=0.4444444444444444 ?- X is 5+4, Y is 5-4. X=9 Y=1 ?- X is 5*4, Y is 2^3. X=20 Y=8
18 Arithmetic Queries ?- X is 234556^100. X = 1058411813164889882981775915184... ?- X is 5/3. X=1.66666667 ?- X is sqrt(3),Y is 3^0.5. X=Y Y=1.7320508075688772 ?- X is 8 mod 3. X=2 ?- Y is 10^3 * (1+1) + 3. Y=2003
19 Recursion % this is fact factorial(0, 1). % this is a rule % the factorial of F is N*F1 % if N>0 and % N1 is N-1 and % the factorial of N1 is F1 factorial(N, F) :- N>0, N1 is N - 1, factorial(N1, F1), F is N * F1. ?- factorial (3, W). W=6 1. factorial(3, W) apply rule 2 2. 3>0, N1 is 3-1, factorial (N1, F1), F is 3 *F1 solve the individual parts true, 2 is 3-1, factorial (2, F1), F is 3*F1 apply rule 2 again 3. 2>0, N2 is 2-1, factorial (N2, F2), F1 is 2 * F2 solve the individual parts true, 1 is 2-1, factorial (1, F1), F1 is 2*F2 apply rule 2 again 4. 1>0, N3 is 1-1, factorial (N3, F3), F2 is 2 * F3 solve the individual parts true, 0 is 1-1, factorial (0, F3), F2 is 1*F3 apply rule 1 again 5. factorial (0, 1) F3 is 1 6. Go back, replace F3 to get F2, then F2 to get F1, then F1 to get F.
Fall 2017 Disclaimer. These slides can only be used as study material for the class CSE240 at ASU. They cannot be distributed or used for another purpose.
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