programmaing in logic apurva patil gayatri kharavlikar meenakshi borse manjiri bankar nikita alai...
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programmaing in logic
Apurva PatilGayatri KharavlikarMeenakshi BorseManjiri BankarNikita AlaiShruti Govilkar
PROgramming in LOGicEmphasis on what rather than
how
Problem in Declarative Form
Basic Machine
Logic Machine
Basic Machine
Logic Machine
LOGIC PROGRAMMING
science of reasoning algorithm = logic + control purely based on rules and facts
artificial intelligence declarative
HISTORYCreated in 1972 by Philippe Roussel
and Alain ColmerauerBased on Robert Kowalski’s procedural
interpretation of Horn clauses
TWO TYPES OF PROGRAMMING LANGUAGES
Procedural (BASIC, Fortran, C++, Java)
Declarative (LISP, Prolog) In procedural programming, we tell the
computer how to solve a problem. In declarative programming, we tell the
computer what problem we want solved.
INTRODUCTION TO PROLOG
Prolog is the most widely used language to have been inspired by logic programming research. Some features:
Prolog uses logical variables. These are not the same as variables in other languages. Programmers can use them as ‘holes’ in data structures that are gradually filled in as computation proceeds.
…MOREClauses provide a convenient
way to express case analysis and nondeterminism.
Sometimes it is necessary to use control features that are not part of ‘logic’.
A Prolog program can also be seen as a relational database containing rules as well as facts.
WHAT A PROGRAM LOOKS LIKE/* At the Zoo */ bigger(elephant, horse).bigger(elephant, horse).bigger(horse, donkey).bigger(donkey, dog).bigger(donkey, monkey).
-Query:?- bigger(donkey, dog).Yesis_bigger(X, Y) :- bigger(X, Z), is_bigger(Z, Y).
PROLOG IS A DECLARATIVE LANGUAGEClauses are statements about what is
true about a problem, instead of instructions how to accomplish the solution.
The Prolog system uses the clauses to work out how to accomplish the solution by searching through the space of possible solutions.
Not all problems have pure declarative specifications. Sometimes extralogical statements are needed.
A Typical Prolog programCompute_length ([],0).Compute_length ([Head|Tail], Length):-
Compute_length (Tail,Tail_length),Length is Tail_length+1.
High level explanation:The length of a list is 1 plus the length of the tail of the list, obtained by removing the first element of the list.
This is a declarative description of the computation.
Fundamentals(absolute basics for writing Prolog Programs)
FactsJohn likes Mary
◦ like(john,mary)Names of relationship and objects
must begin with a lower-case 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.
More facts
Predicate Interpretation
valuable(gold) Gold is valuable.
owns(john,gold) John owns gold.
father(john,mary) John is the father of Mary
gives (john,book,mary)
John gives the book to Mary
RulesStatements about objects and their
relationshipsExpess
◦ 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).
Syntax<head> :- <body>Read ‘:-’ as ‘if’.E.G.
◦likes(john,X) :- likes(X,cricket).◦“John likes X if X likes cricket”.◦i.e., “John likes anyone who likes
cricket”.Rules always end with ‘.’.
Question Answering in presence of rulesFacts
◦male (ram).◦male (shyam).◦female (sita).◦female (gita).◦parents (shyam, gita, ram).◦parents (sita, gita, ram).
Question Answering: Y/N type: is sita the sister of shyam?
female(sita)parents(sita,M,F) parents(shyam,M,F)
parents(sita,gita,ram)parents(shyam,gita,ram)
success
?- sister_of (sita, shyam)
Complete Syntax of Terms Term
Constant VariableCompound Term
Atom Numberalpha17gross_payjohn_smithdyspepsia+=/=’12Q&A’
01571.6182.04e-27-13.6
likes(john, mary)book(dickens, Z, cricket)f(x)[1, 3, g(a), 7, 9]-(+(15, 17), t)15 + 17 - t
XGross_payDiagnosis_257_
Names an individual Stands for an individualunable to be named when program is written
Names an individualthat has parts
Compound Terms
parents(spot, fido, rover)
The parents of Spot are Fido and Rover.
Functor (an atom) components (any terms)
It is possible to depict the term as a tree:
parents
roverfidospot
VariablesVariables always start with an
upper case alphabetic character or an underscore
◦?- likes (john,X).◦?- likes (john, Something).
But not ◦?- likes (john,something)
ConjunctionsUse ‘,’ and pronounce it as and.Example
◦ Facts: likes(mary,food). likes(mary,tea). likes(john,tea). likes(john,mary).
?- likes(mary,X),likes(john,X).
Both facts and rules are predicate definitions.
‘Predicate’ is the name given to the word occurring before the bracket in a fact or rule:
parent(jane,alan).
By defining a predicate you are specifying relationship between objects.
Predicate Definitions
Predicate name
ClausesPredicate definitions consist of clauses.
e.g. mother(jane,alan). = Fact parent(P1,P2):- mother(P1,P2). = Rule
A clause consists of a headand sometimes a body.
Facts don’t have a body because they are always true.
head body
ArgumentsA predicate head consists of a predicate name
and sometimes some arguments contained within brackets and separated by commas.
mother(jane,alan).
Arguments also consist of terms, which can be:Constants e.g. jane,Variables e.g. Person1, orCompound terms
Predicate name Arguments
ArityThe number of arguments a predicate
has is called its arity.
greetings is a predicate with no arguments.The arity of greetings is zero =
greetings/0
By including more arguments predicates can be made more specific .greetings(hamish) = greetings/1
The predicate can then behave differently depending on the arguments passed to it.
Backtracking (an inherent property of prolog programming)
likes(mary,X),likes(john,X)
likes(mary,food)likes(mary,tea)likes(john,tea)likes(john,mary)
1. First goal succeeds. X=food2. Satisfy likes(john,food)
Backtracking (continued)
Returning to a marked place and trying to resatisfy is called Backtracking
likes(mary,X),likes(john,X)
likes(mary,food)likes(mary,tea)likes(john,tea)likes(john,mary)
1. Second goal fails2. Return to marked place and try to resatisfy the first goal
Backtracking (continued)
likes(mary,X),likes(john,X)
likes(mary,food)likes(mary,tea)likes(john,tea)likes(john,mary)
1. First goal succeeds again, X=tea2. Attempt to satisfy the likes(john,tea)
Backtracking (continued)
likes(mary,X),likes(john,X)
likes(mary,food)likes(mary,tea)likes(john,tea)likes(john,mary)
1. Second goal also suceeds2. Prolog notifies success and waits for a reply
Structure of Programs
Programs consist of procedures.Procedures consist of clauses.Each clause is a fact or a rule.Programs are executed by posing queries.
An example…
Example
elephant(george).elephant(mary).elephant(X) :- grey(X), mammal(X), hasTrunk(X).
Procedure for elephant
Predicate
Clauses
Rule
Facts
Example
?- elephant(george).
yes
?- elephant(jane).
no
Queries
Replies
Body of a (rule) clause contains goals.
likes(mary, X) :- human(X), honest(X).
Head Body
Goals
Interpretation of ClausesClauses can be given a declarative reading or a
procedural reading.
H :- G1, G2, …, Gn.
“That H is provable follows from goals G1, G2, …, Gn being provable.”
“To execute procedure H, the procedures called by goals G1, G2, …, Gn are executed first.”
Declarative reading:
Procedural reading:
Form of clause:
EXAMPLE
berkshire
wiltshire
surrey
hampshire sussex
kent
How to represent this relation?Note that borders are symmetric.
(a) Representing a symmetric relation.(b) Implementing a strange ticket condition.
Contd...
border(sussex, kent).border(sussex, surrey).border(surrey, kent).border(hampshire, sussex).border(hampshire, surrey).border(hampshire, berkshire).border(berkshire, surrey).border(wiltshire, hampshire).border(wiltshire, berkshire).
This relation representsone ‘direction’ of border: What about the other?
(a) Say border(kent, sussex).border(sussex, kent).
(b) Sayadjacent(X, Y) :- border(X, Y).adjacent(X, Y) :- border(Y, X).
Contd...
valid(X, Y) :- adjacent(X, Z), adjacent(Z, Y)
Now a somewhat strange type of discount ticket. For theticket to be valid, one must pass through an intermediate county.
A valid ticket between a start and end county obeys the following rule:
Contd...border(sussex, kent).border(sussex, surrey).border(surrey, kent).border(hampshire, sussex).border(hampshire, surrey).border(hampshire, berkshire).border(berkshire, surrey).border(wiltshire, hampshire).border(wiltshire, berkshire).
adjacent(X, Y) :- border(X, Y).adjacent(X, Y) :- border(Y, X).
?- valid(wiltshire, sussex).?- valid(wiltshire, kent).?- valid(hampshire, hampshire).?- valid(X, kent).?- valid(sussex, X).?- valid(X, Y).
valid(X, Y) :-adjacent(X,
Z), adjacent(Z, Y)
How to save prolog file:Save as Filename.plConflict with PerlAlternative extension can be
filename.pro or filename.prNo capitalsC:/MyDocument //errorC:/mydocumentTo exit prolog- ‘halt’
Different editors:SWI Prolog
◦Extra libraries◦Built in predicates
GNU Prolog◦Support constraints logic
programmingVisual Prolog
◦A complete development environment for object oriented extension to prolog
And many more…
SIGNIFICANT FEATURESSimplicity
Regularity
Intelligent systems
Expert systems
Natural language systems
Relational database systems
ADVANTAGES:-
Logic based languages are able to represent the real world more accurately.
Prolog is able to derive new rules from the existing rules contained within the knowledge base.
Strong ties to formal logicMany algorithms become trivially
simple to implement
DISADVANTAGES:-
-It can be very difficult to design a database that accurately represents relationships.
Prolog is not best suited to solving complex arithmetical computations.
Complicated syntaxDifficult to understand programs at first sight
Prolog programs are not best suited to the current PC architecture (sequential execution) and are best optimised on parallel architectures (fifth generation computers).
APPLICATIONS:
Target User:◦Expert Systems (Knowledge
Representation and Inferencing)◦Natural Language Processing◦Relational Databases◦Artificial intelligence
Thank u..!!
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