Prolog is a logic programming language based on first-order predicate logic. It was developed in the late 1960s and early 1970s, and the first efficient version was created in the mid-1970s. Prolog is declarative rather than imperative, and uses logic rules, facts, queries, automatic backtracking, and recursion to solve problems. It is widely used for artificial intelligence and natural language processing tasks. Prolog programs consist of facts and rules, and reasoning is done by resolving queries against the facts and rules through a process of backtracking.

1. Prolog programming language

2. History
• Kowalski: late 60’s Logician who showed logical proof can support
computation.
• Colmerauer: early 70’s Developed early version of Prolog for
natural language processing, mainly multiple parses.
• Warren: mid 70’s First version of Prolog that was efficient.
• The official ISO standard for Prolog was published in 1996.

3. • Prolog is the most popular language of the logic programing
languages.
• It is goal based language, it has automatic backtracking and
uses recursion.
• Prolog stands for programmation en logique", or programming
in logic.“
• Emphasis on what rather than how
• It is widely used in the field of AI
Introduction

4. Introduction

5. Characteristics
• Prolog approximates first-order logic.
• Every program is a set of Horn clauses.
• Inference is by resolution.
• Search is by backtracking with unification.
• Basic data structure is term or tree.
• Variables are unknowns not locations.
• Prolog does not distinguish between inputs and outputs. It solves
relations/predicates.

6. Features

7. Features
Backtracking-
• prolog stores data in tree.
• It uses depth first search to find answers.
• In its attempt to prove a goal, Prolog sometimes goes
down a dead-end, at which point it needs to backtrack.

8. Features
• Prolog is major example of fourth generation programming
language supporting the declarative programming paradigm.
• In a declarative language the programmer specifies a goal to
be achieved the prolog system works out hoe to achieve it.
• Relational databases owe something to prolog

9. Current implementations
• There are several popular Prolog interpreters available. They
include:
• GNU Prolog (http://pauillac.inria.fr/vdiaz/gnuprolog/)
• SWI-Prolog (http://www.swi-prolog.org/)
• Visual Prolog
(http://www.visualprolog.com/vip6/Download/Default.htm)
• BProlog
(http://www.cad.mse.kyutech.ac.jp/people/zhou/bpr
• olog.html)

10. Weaknesses of prolog
• Lack of structure
• Issues with readability of Prolog code
• serious implications for the readability and
• declarativeness of code due to cut predicate (!).
• Inefficiency of Prolog code
• Logical imperfectness

11. Fundamentals
• Facts
• Rules
• Query
• Unification
• Resolution
• Backtracking
• Cuts and negations

12. Facts
• Facts are statements about what is true about a problem,
instead of instructions how to accomplish the solution.
• The Prolog system uses the facts to work out how to accomplish
the solution by searching through the space of possible
solutions.
• It is defined by an identifier followed by an n-tuple of constants.
• A relation identifier is referred to as a predicate
• When a tuple of values is in a relation we say the tuple satisfies
the predicate.

13. Syntax for facts declaration
• Names of relationship and objects must begin with a lowercase
letter.
• Relationship is written first (typically the predicate of the
sentence).
• Objects are written separated by commas and are enclosed by a
pair of round brackets.
• The full stop character ‘.’ must come at the end of a fact.

14. Rules
• Specifies under what conditions a tuple of values
satisfies a predicate.
• The basic building block of a rule is called an atom
• Atom :- Atom1, ..., Atomn
If each of Atom1,...,Atomn is true, then Atom is also
true.

15. Rules
• Rules specify:
• If-then conditions
• I use an umbrella if there is a rain
• use(i, umbrella) :- occur(rain).
• Generalizations
• All men are mortal
• mortal(X) :- man(X).
• Definitions
• An animal is a bird if it has feathers
• bird(X) :- animal(X), has_feather(X).