Prolog (present)

Prolog

Logic Programming Language

Prepared by :
Chin Joo Ee & Tan Geok Fah

A computer programming language
based on mathematical logic.
 Used for writing programs that
model human logic and decision
making.
 PROLOG has an elegant formulation.
 Prolog is a logical and declarative
programming language.

 The first of the huge family of logic
programming languages.
 Invented by Alain Colmerauer and Phillipe
Roussel at the University of Aix-Marseille
in 1971.

Alain Colmerauer

 It was first implemented 1972 in
ALGOL-W.
 Early implementations
→included C-Prolog, ESLPDPRO, Frolic,
LM-Prolog, Open Prolog, SB-Prolog,
UPMAIL Tricia Prolog.
 In 1998, the most common Prologs in use
are Quintus Prolog, SICSTUS Prolog, LPA
Prolog, SWI Prolog, AMZI Prolog, SNI
Prolog.

 Prolog was designed originally for natural-
language processing but has become one of
the most widely used languages for
artificial.
 The first versions had no user-defined
functions and no control structure other
than the built-in depth-first search with
backtracking.
 Early collaboration between Marseille and
Robert Kowalski at University of Edinburgh
continued until about 1975.

Robert Kowalski

 A rich collection of data structures in the
language and human reasoning
 A powerful notation for encoding end-user
applications
 It has its logical and declarative aspects,
interpretive nature, compactness, and
inherent modularity.

 In a logic language
✎consisting of Horn Clauses
✎enter into database by the
programmer
 Unlike most common programming languages.
 In a declarative language
✎the programmer specifies a goal to be
achieved
✎the Prolog system works out how to
achieve it

 To simplify the resolution process in Prolog,
statements must be expressed in a
simplified form, called Horn clauses.
 Each statement (clause) has (at most) one
term on the left hand side of an implication
symbol ( :- ).
 Each statement has a conjunction of zero
or more terms on the right hand side.

 Facts
 Rules
 Queries
 A collection of facts and rules is called a
knowledge base (database)
 A collection of facts and queries which
describe some collection of relationship.

Example facts:
 male(adam). female(anne). parent(adam,barney).

Example rules:
1. son(X,Y) :- parent(Y,X) ,
 The first rule is read as follows:
→For all X and Y, X is the son of Y if there exists X &
Y (X,Y)
→such that Y is the parent of X and X is male.

2. male(X), daughter(X,Y) :- parent(Y,X) , female(X)
 The second rule is read as follows:
→For all X and Y, X is the daughter of Y if
there exists X & Y
→such that Y is the parent of X and X is female.

 To make things crystal clear, let’s first
precise about the basic characters at
disposal.
 The upper-case letters are A, B, …, Z
 The lower-case letters are a, b, …, z
 The digits are 0, 1, 2, …, 9
 In addition, the _ symbol, which is called
underscore, & some special characters,
which include characters such as +, -,*, /,
<, >, =,:, &, ~.
 The blank space is also a character, but a
rather unusual one, being invisible.

 To run a Prolog program, the user must ask a
question (goal) by stating a theorem
( asserting a predicate) which the prolog
interpreter try to prove.
 If the predicate contains variables, the
interpreter prints the values of the variables
used to make the predicate true.
 The interpreter uses backward chaining to
prove a goal. It begins with the thing it is try
to prove, and work backwards looking for
things that would imply it, until it gets the
facts.

 Logical relationships are asserted, and
Prolog is used to determine whether or not
certain statements are true, and if true,
what variable bindings make them true.
 This leads to a very declarative style of
programming.
 It is a program that is efficient to use if
one want to work out problems by
representing objects symbolically according
to a type of relationships.
 It can used in software engineering.

 intelligent data base retrieval
 natural language understanding
 expert systems
 specification language
 machine learning
 robot planning
 automated reasoning
 problem solving
 adventure game
 customer order entry business application

 programs which perform
Intelligent
useful tasks by utilizing
Systems artificial intelligence
techniques

 intelligent systems which Expert
reproduce decision-making at Systems
the level of a human expert

Natural Language  which can analyses and
Systems respond to statements
made in ordinary language
as opposed to approved
keywords or menu
selections.

ease of representing
knowledge
natural support of non-
determinism
natural support of pattern-
matching
natural support of meta-
programming

meaning of programs is
independent of how they are
executed
simple connection between
programs & computed answers
& specifications
no need to distinguish programs
from databases

 Initially, due to insufficient investment in
complimentary technologies, users were poorly
served.
 In the beginning, poor facilities for supporting
arithmetic, types, etc. had a discouraging
effect on the programming community.
 There is no adequate way of representing
computational concepts found in built-in
mechanisms of state variables (as is usually found
in conventional languages).
 Some programmers always have, & always will
prefer the overtly operational nature of machine
operated programs, since they prefer the active
control over the 'moving parts'.

Description
This program demonstrates the text output
function of the Sample programming language
by displaying the message "Hello world!”
Source Code
// the main program (this is a comment)
Hello:-
nl,
write('Hello world!' ).
}

THANK YOU …

Bye Bye ~

Prolog (present)

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