ProLog (Artificial Intelligence) Introduction

Logic Programming (ProLog), SWI Prolog, Bin-prolog, Prolog++, PDC Visual Prolog, ProLog Introduction, ProLog Paradigm, ProLog Syntax, proLog Example Artificial Intelligence, Propositional Calculus, Expert System in ProLog

1. PROLOG PRO gramming in LOG ic A Brief Introduction

2. Compilers PDC Visual Prolog SWI Prolog Bin-Prolog K-Prolog Prolog ++ http://swish.swi-prolog.org

3. PRO-LOG Programming in Logic 1975 , Phillippe Roussell Predicate Calculus Declarative Language Predicates and Rules Inference Mechanism

4. PROLOG Paradigm PROgramming in LOGic Draw inferences from facts and rules PROLOG is declarative - specify facts and logical relationships Non-procedural: "what", not "how". (we specify the problem but not the solution) Database language with automated search and the ability to follow general rules. symbolic - symbols are used to represent objects high level - contains a built-in problem solving mechanism PROLOG Programming (When we program in ProLog we need to provide following three things) Declaring some facts about objects and their relationships Defining some rules about objects and their relationships Asking questions about objects and their relationships

5. PROLOG Paradigm The PROLOG Programmer Loads facts and rules into the database. Makes queries to the database to see if a fact is: in the database or can be implied from the facts and rules therein Prolog Database Facts + Rules Query

6. System Interaction Problem solving in PROLOG 1. insert facts and rules into the database 2. ask questions (queries) based on the contents of the database Facts Used to represent unchanging information about objects and their relationships. Only facts in the PROLOG database can be used for problem solving. Insert facts into the database by, typing the facts into a file and loading (consulting) the file into a running PROLOG system

7. System Interaction Queries Retrieve information from the database by entering QUERIES A query, is a pattern that PROLOG is asked to match against the database has the syntax of a compound query may contain variables A query will cause PROLOG to look at the database try to find a match for the query pattern execute the body of the matching head return an answer

8. Logic Programming Logic programming is a form of declarative programming A program is a collection of axioms Each axiom is a Horn clause of the form: H :- B1, B2, ..., Bn. where H is the head term and Bi are the body terms Meaning H is true if all Bi are true

9. Basic Proof technique - modus ponens A -> B A --------- B

10. Prolog Uses backward chaining More efficient than forward chaining for larger collections of axioms Applications : expert systems, artificial intelligence, natural language understanding, logical puzzles and games

11. PROLOG Paradigm Examples (Facts) English PROLOG “A dog is a mammal” isa(dog, mammal). “A sparrow is a bird” isa(sparrow, bird).

12. PROLOG Paradigm Examples (Rules) English PROLOG “Something is an animal animal(X) :- isa(X,mammal). if it is a mammal or a bird” animal(X) :- isa(X, bird).

13. PROLOG Paradigm Examples (Queries) English PROLOG “is a sparrow an animal?” ?- animal(sparrow). answer: “yes” yes “is a table an animal?” ?- animal(table). answer: “no” no “what is a dog?” ?- isa(dog, X). answer: “a mammal” X = mammal

14. PROLOG syntax Constants Atoms Alphanumeric atoms - alphabetic character sequence starting with a lower case letter Examples: apple a1 apple_cart Quoted atoms “String” - sequence of characters surrounded by single quotes Examples: ‘Apple’ ‘hello world’ Symbolic atoms - sequence of symbolic characters Examples: & < > * - + >> Special atoms Examples: ! ; [ ] {} Numbers Integers and Floating Point numbers Examples: 0 1 9821 -10 1.3 -1.3E102

15. PROLOG syntax Variable Names a sequence of alphanumeric characters beginning with an upper case letter or an underscore Examples: Anything _ var X _ Compound Terms (structures) an atom followed by an argument list containing terms. The arguments are enclosed within brackets and separated by commas Example: isa (dog, mammal)

16. Prolog syntax The names of all relationships and objects must begin with a lower case letter. For example studies, ali, programming The relationship is written first and the objects are enclosed within parentheses and are written separated by commas. For example studies(ali, programming) The full stop character ‘.’ must come at the end of a fact. Order is arbitrary but it should be consistent

17. Example Program with three facts and one rule: rainy( columbo ). rainy( ayubia ). cold( ayubia ). Rule: snowy(X ) :- rainy(X), cold(X). Query and response: ?- snowy( ayubia ). yes Query and response: ?- snowy( columbo ). no Query and response: ?- snowy( lahore ). No ?- snowy(C). C = ayubia because rainy(ayubia) and cold(ayubia) are sub-goals that are both true facts in the database snowy(X) with X=columbo is a goal that fails, because cold(X) fails, triggering backtracking

18. snowy(C) snowy(X) AND rainy(X) cold(X) C = X rainy(columbo) rainy(ayubia) X = columbo X = ayubia cold(ayubia) C = X = ayubia C = ayubia rainy(columbo). rainy(ayubia). cold(ayubia). snowy(X) :- rainy(X), cold(X). ?- snowy(C). C = ayubia OR

19. Logic Representation : Propositional Calculus Propositional Logic Boolean statements Logic connectives      Example – a family Atomic statements p : Ahmed is father of Belal q : Ahmed is brother of Aslam r : Aslam is uncle of Belal Complex statements  Statement Logic  p Ahmed is not father of Belal p  q Ahmed is father of Belal or Ahmed is brother of Aslam p  q  r If Ahmed is father of Belal and brother of Aslam then Aslam is uncle of Belal

20. Prolog Programming Predicate Calculus Predicates (Facts) man(Ahmed) father(Ahmed, Belal ) brother( Belal , Chand) brother(Chand, Delawar ) owns( Belal , car) tall( Belal ) hates(Ahmed, Chand) family() Formulae X,Y,Z(man(X)  man(Y)  father(Z,Y)  father(Z,X)  brother(X,Y)) Variables X, Y and Z Constants Ahmed, Belal , Chand, Delawar and car Prolog code Predicates man(symbol) father(symbol, symbol) brother(symbol, symbol) owns(symbol, symbol) tall(symbol) hates(symbol, symbol) family() Clauses man( ahmed ). father( ahmed , belal ). brother( ahmed , chand ). owns( belal , car). tall( belal ). hates( ahmed , chand ). family(). Rule: brother(X,Y ):- man(X), man(Y), father(Z,Y), father(Z,X). Goal brother( ahmed,belal ).

21. Sections of Prolog Program (1-3) Predicates Declarations of Relations or Rules Just like function prototype (declaration). Zero or more arguments Example Predicates man(symbol) family() a_new_predicate (integer, char)

22. Sections of Prolog Program (2-3) Clauses Definition(s) of Predicate = Sentence OR Phrase Types Rules (function definitions) 0 or more conditions (statements) Facts 0 conditions All parameters constant Examples Fact brother(ahmed, chand). Rule brother(X,Y):- man(X), man(Y), father(Z,Y), father(Z,X).

23. Sections of Prolog Program (3-3) Goal Goal of inference Only and exactly one instance The only tentative section of the program The main() of prolog Goal truth value = output of program Syntactically and Semantically just another clause Empty, simple (one goal), or compound (sub-goals) Examples Goal brother(X,chand). <or> brother(ahmed,chand). Goal brother(X,chand), father().

24. Sample Program Update domains person = symbol predicates nondeterm father(person,person) nondeterm brother(person,person) nondeterm cousin(person,person) nondeterm grandfather(person,person) clauses father(a,b). father(a,c). father(a,d). father(b,e). father(b,f). father(b,g). father(c,h). father(c,i). father(d,j). father(d,k). brother(X,Y):- X<>Y, father(Z,X), father(Z,Y). cousin(X,Y):- father(A,X), father(B,Y), brother(A,B). grandfather(X,Y):- father(Z,Y), father(X,Z). goal cousin(X,Y).

25. Prolog Variables Constant placeholders (NOT variables) Bounded once Loosely typed Start with Capital letter or underscore Examples brother( ahmed , Ahmed) brother( ahmed , _x) Brother( ahmed , X) Anonymous variable The _ Some value that isn’t required Example brother( ahmed , _)

26. Expert system A simple medical expert system relieves(Drug, Symptom). relieves(aspirin, headache). relieves(aspirin, moderate_pain ). relieves(aspirin, moderate_arthritis ). relieves( aspirin_codine_combination , severe_pain ). relieves( cough_cure , cough). relieves( pain_gone , severe_pain ). relieves( anti_diarrhea , diarrhea). relieves( de_congest , cough). relieves( de_congest , nasal_congestion ). relieves( penicilline , pneumonia). relieves( bis_cure , diarrhea). relieves( bis_cure , nausea). relieves( new_med , headache). relieves( new_med , moderate_pain ). relieves( cong_plus , nasal_congestion ).

27. aggravates(Drug, Condition). aggravates(aspirin, asthma). aggravates(aspirin, peptic_ulcer). aggravates(anti- diarrhea , fever). aggravates(de_congest, high_blood_pressure). aggravates(de_congest, heart_disease). aggravates(de_congest, diabetes). aggravates(de_congest, glaucoma). aggravates(penicilline, asthma). aggravates(de_congest, high_blood_pressure). aggravates(bis_cure, diabetes). aggravates(bis_cure, fever).

28. should_take (Person, Drug) :- complains_of (Person, Symptom), relieves(Drug, Symptom), not( unsuitable_for (Person, Drug )). //conjunction of three classes. unsuitable_for (Person, Drug) :- aggravates(Drug, Condition), suffers_from (Person, Condition). complains_of ( ali , headache). suffers_from ( ali , peptic_ulcer ). ?- should_take ( ali , Drug). Drug = new_med ;

29. Books Prolog Programming for AI by Ivan Bratko Visual Prolog; Language Tutorial by PDC