Logic Programming Dr. Yasser Nada Fall 2010/2011 Lecture 1 1 Logic Programming

Text Book Prolog Programming, A First Course, by Paula Brna, 2001 References: – Leon Starling and Ehud Shapiro, The art of Prolog – Ivan Brotko, Prolog Programming for Artificial Intelligence Logic Programming

Course Description This course will introduce the theory and concepts of logic programming. Prolog will be studied as a logic programming approach for declarative logic programming. 3 Logic Programming

Course Objectives Upon completion of the course, student should: – Knowledge of concepts and theories of logic programming. – Become familiar with Prolog language syntax. – Be able to solve problems in Prolog. – Be able to use knowledge in a suitable form to be used in Prolog language.. 4 Logic Programming

Course Policy Students are expected to participate and attend the class in time. Students are responsible to submit assignments in time. Exams will be a combination of lectures in class and homework assignments. Late homework submission will be subject to penalties. If an assignment is submitted late, a penalty of 10 percent of that assignment's grade will be assessed for each day it is late. A homework paper will not be accepted after graded papers have been returned, after a solution has been distributed, or after the final examination. 5 Logic Programming

Absence Policy Students absent that exceeds (25% lectures) are being considered dropped from the course. After 3 lectures absent a warning is issued for the student. After another 3 lectures absent student will be dropped from the class. 6 Logic Programming

Examination There will be no makeup exams except under emergencies. If a student cannot attend the exam, then student must make arrangement with the instructor prior to the planned absence. The emergency makeup exam will be either written or oral. 7 Logic Programming

Grading 8 Logic Programming Assignment10% Attendance10% Midterm30% Final50%

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What is Logic Programming Two types of programming languages: – Imperative languages (C, C++, VB, C#, Java, …). – Declarative languages (prolog, lisp, …). Logic programming is a type of programming called declarative programming. 10 Logic Programming

Imperative Languages They are also called procedural languages. Programmer gives all steps to solve a problem. He must know an algorithm to solve a problem. Example: find average of list of numbers: Input total Input number Average = total/number Print Average 11 Logic Programming

Declarative Languages Programmer describe the problem without the control flow, then the system will solve the problem. Programmer must know the relations between objects to solve the problem. Programmer does not need to know an algorithm to solve the problem. Declarative languages consists of: – Program or theory. – Computation which is deduction. 12 Logic Programming

First Order Predicate Represent relation between objects: own(ahmed, car). friend(ali, ahmed). father(sami, ali). brother(kareem, ali). 13 Logic Programming

It is a declarative language (not completely declarative) based on first order logic. Prolog means Programming in Logic. It consists of: – Facts. – Rules. – Goal Used in AI: NLP, expert systems, games, automated answering system, …. 14 Prolog Logic Programming

Prolog Program consist of: – Facts: asserts a property to an object, or relation between two or more objects: parent(ali, salem). own(ali, car). – Rules: allow to infer a relationship or a property based on a precondition: parent(X,Y) :- father(F,X), father(P,Y). – Goal: Query or questions asked by user. parent(ali, Y). 15 Prolog Logic Programming

Atom is – a sequence of alphanumeric characters – usually starting with lower case letter – or, a string enclosed in single quotes – They represent constants. Examples: – ali, salem, a, b, c, a1, a2, b3, c5, … – ‘Mr. Ali’, ’Dr. Sultan’ 16 Atoms Logic Programming

A variable is a sequence of alphanumeric characters usually starting with an uppercase letter Examples: X, Y, Z, Parent, Child, Foo, X1, Y1, X2, X5, X6, …. 17 Variables Logic Programming

A predicate has the form – p(t1,...,tn) – where p is an atom and t1...tn are variables or atoms. – n is the number of arguments of predicate p (written as p/n which represents the signature of predicate). – Predicates can be of 0-arg, 1-arg, 2-arg, … Examples: – father(ali, ahmed). 18 Predicates Logic Programming

like(ali, car). like(ahmed, car). father(salem, ali). father(salem, ahmed). brother(X,Y) :- father(P,X), father(P,Y). friend(X,Y) :- like(X,C), like(Y,C). 19 Prolog Program Example Logic Programming Predicate name Predicate arguments Predicate End if and

A goal is a conjunction of predicates – p(X,Y),q(Y,Z),t(Z,W). – A goal is the question or query asked by the user. Prolog will try to find an answer for the goal. 20 Goals Logic Programming

Given a goal, Prolog searches for answer(s): – “yes” (possibly with answer substitution) – “no” (if no answer or no more answer found). – Substitutions are bindings of variables that make goal true. 21 Answers Logic Programming

?- father(X,ali). – X = salem ? ; – no ?- father(X,Y), brother(Y,Z). – X = salem, Y = ali, Z = ahmed – yes – ? ; – X = salem, Y=ahmed, Z=ali – Yes – ? ; – no 22 Examples Logic Programming male(ali). male(ahmed). male(salem). father(salem, ali). father(salem, ahmed). brother(X,Y) :- father(P,X), father(P,Y), male(X), male(Y).

A rule is an assertion of the form – p(ts) :- q(ts’),..., r(ts’’). – where ts, ts’, ts’’ are atoms or variables “p(ts) holds if q(ts’) holds and... And r(ts’’) holds” Example: – brother(X,Y) :- father(Z,X), father(Z,Y). 23 Rules Logic Programming

You can try prolog by downloading prolog compiler: – Ciao: – Choose Windows version, For Windows Vista: current version For Windows XP: select version Ciao- 1.10p5Win32.zip 24 Prolog Logic Programming

After downloading ciao-1.10pWin32.zip, extract it in C:\ Then goto C:\Ciao-1.10p5Win32 Double click on the file: install.bat Then type ciaosh at the DOS prompt, the prolog prompt appears: ?- 25 Ciao installation under Windows XP Logic Programming

After downloading CiaoDE XXXX.exe, double click on it to run. At the desktop you will find a file: ciaosh shortcut. Double click on it and the Prolog prompt appears: ?- 26 Ciao installation under Windows Vista Logic Programming

Comments – % single line comment – /* multiple line comment */ To quit Ciao, type – ?- exit. – (or just control-D) 27 Miscellaneous Logic Programming