Logic Programming

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Logic Programming
PROLOG

• Dr. Yasser Nada
• Fall 2010/2011
• Lecture 1

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Text Book

• Prolog Programming, A First Course, by Paula
  Brna, 2001
• References
• Leon Starling and Ehud Shapiro, The art of
  Prolog. 1989.
• Ivan Brotko, Prolog Programming for Artificial
  Intelligence. 1986.

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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.

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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..

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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.

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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.

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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.

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Grading
Assignment 10
Attendance 10
Midterm 30
Final 50
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Introduction
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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.

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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

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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.

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First Order Predicate

• Represent relation between objects
• own(ahmed, car).
• friend(ali, ahmed).
• father(sami, ali).
• brother(kareem, ali).

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Prolog

• 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, .

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Prolog

• 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).

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Atoms

• 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

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Variables

• 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,
  .

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Predicates

• 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).

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Prolog Program Example

• 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).

Predicate name
Predicate arguments
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Predicate End
and
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Goals

• 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.

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Answers

• 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.

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Examples
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).

• ?- father(X,ali).
• X salem ?
• no
• ?- father(X,Y), brother(Y,Z).
• X salem, Y ali, Z ahmed
• yes
• ?
• X salem, Yahmed, Zali
• Yes
• ?
• no

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Rules

• 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).

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Prolog

• You can try prolog by downloading prolog
  compiler
• Ciao http//clip.dia.fi.upm.es/Software/Ciao/Late
  st/download.html
• Choose Windows version,
• For Windows Vista current version 1.13.0.
• For Windows XP select version Ciao-1.10p5Win32.zi
  p

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Ciao installation under Windows XP

• 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 ?-

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Ciao installation under Windows Vista

• After downloading CiaoDE-1.13.0-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
• ?-

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Miscellaneous

• Comments
• single line comment
• / multiple
• line
• comment /
• To quit Ciao, type
• ?- exit.
• (or just control-D)

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Logic Programming