Prolog,Prolog Programming IN AI.pdf

Prolog, Prolog Programming IN AI. Prolog is an Artificial Intelligence programming language. Prolog is a logic programming language associated with artificial intelligence and computational linguistics. Its applications include natural language understanding and expert systems. Prolog is notably a so-called nonprocedural, or declarative, language.

1. Prolog Programming

2. Introduction
Prolog
Prologisalogicprogramminglanguage.It
hasimportantroleinartificialintelligence.
Unlikemanyotherprogramminglanguages,
Prologisintendedprimarilyasadeclarative
programminglanguage.Inprolog,logicis
expressedasrelations(calledasFactsand
Rules).Coreheartofprologliesat
thelogicbeingapplied.Formulationor
Computationiscarriedoutbyrunninga
queryovertheserelations.
4
Prolog

3. Prologprogramissimplybasedonpredicate
logicknownasHornclause.Inprolog,we
composetheprogramusingfactsandrulesand
weposeaqueryonquerypromptaboutthe
factsandrulesweinserted.
5Prolog Programming Basics
HornClause:Hornclauseconsistsofhead(lefthand
side)andbody(righthandside).Headcanhave0or1
predicateandbodycanhavelistofpredicates.That
meansLHShasonlysingleliteralandRHScanhave
morethanoneliterals.
head:-body.

4. What is Prolog?
»PrologorPROgramminginLOGicsisalogicaland
declarativeprogramminglanguage.Itisonemajorexample
ofthefifthgenerationlanguagethatsupportsthe
declarativeprogrammingparadigm.Thisisparticularly
suitableforprogramsthatinvolvesymbolicornon-
numericcomputation.Thisisthemainreasontouse
PrologastheprogramminglanguageinArtificial
Intelligence,wheresymbolmanipulationandinference
manipulationarethefundamentaltasks.
»InProlog,weneednotmentionthewayhowoneproblem
canbesolved,wejustneedtomentionwhattheproblem
is,sothatPrologautomaticallysolvesit.However,inProlog
wearesupposedtogivecluesasthesolutionmethod.
6

5. Programminglanguagesareoftwokinds:
Procedural(BASIC,Fortran,C++,Pascal,
Java);
Declarative(LISP,Prolog,ML).
Inproceduralprogramming,wetellthe
computerhowtosolveaproblem.
Indeclarativeprogramming,wetellthe
computerwhatproblemwewantsolved.
SWI-PrologoffersacomprehensivefreeProlog
environment.Sinceitsstartin1987,SWI-Prolog
developmenthasbeendrivenbytheneedsofreal
worldapplications.SWI-Prologiswidelyusedin
researchandeducationaswellascommercial
applications.
PrologwasoriginallydesignedtobeanAIlanguage,
anditisverywellsuitedforexpertsystems,planning
systemsandsimilarAIapplications.
Logic Programming: Prolog
SWI -Prolog
ThelogicprogramminglanguagePROLOG(ProgrammationenLogique)
wasconceivedbyAlainColmerauerattheUniversityofAix-Marseille,
France,wherethelanguagewasfirstimplementedin1973.PROLOGwas
furtherdevelopedbythelogicianRobertKowalski,amemberoftheAIgroup
attheUniversityofEdinburgh.

6. 8
Machine
Logical Programming
Machine
Answer
Int main()
{
Procedure 1 ()
Procedure 2 ()
return
}
Knowledge
Base
Queries
Functional Programming
Prolog Interpreter
Facts & Rules

7. Rulesareextinctionsoffacts
thatcontainconditional
clauses.Tosatisfyarule
theseconditionsshouldbe
met.
Rules
Andtorunaprolog
program,weneedsome
questions,andthose
questionscanbeanswered
bythegivenfactsandrules
Questions
Factsarestatements
thatdescribeobject
propertiesorrelations
betweenobjects.
Thefactispredicatethat
istrue,forexample,ifwe
say,“Tomisthesonof
Jack”,thenthisisafact.
Facts
Prolog language basically has three different elements −
Facts Rules Queries

8. Prolog Syntax
The syntax of Prolog is as follows:
relationship(object1,object2)

9. Prolog
»Example:
»“Arslan owns the book”
»Owns (arslan, book) relationship(object1, object2)
»The relationship has a specific order, arslan own the
book, but the book dose not owns arslan, and this
relationship and its representation above called fact.
11

10. English Predicate CalculusProlog
If → :-
Not ~ Not
Or V ;
and ^ ,
female,Male,X,Y,mother_of,_father,Pro34
Variableisastring.Thestringcanbeacombinationoflowercaseor
uppercaseletters.Thestringcanalsocontainunderscorecharacters
thatbeginwithanunderscoreoranupper-caseletter.Rulesfor
formingnamesandpredicatecalculusarethesame.
Usingthefollowingtruth-functionalsymbols,theProlog
expressionsarecomprised.Thesesymbolshavethesame
interpretationasinthepredicatecalculus.
Symbols
Variables

11. 13
Afactislikeapredicateexpression.Itisusedtoprovideadeclarativestatementaboutthe
problem.InaPrologexpression,whenavariableoccurs,itisassumedtobeuniversally
quantified.Factsarespecifiedintheformofthehead.Headisknownastheclausehead.Itwill
takeinthesamewayasthegoalenteredatthepromptbytheuser.
Facts
cat(momo). /*momoisacat*/
dog(pulu). /*puluisadog*/
likes(arslan, jolie). /*ArslanlikesJolie*/
not(likes(Jolie,pasta)). /*Joliedoesnotlikepasta*/
Forexample:
Queries
InProlog,thequeryistheactionofaskingtheprogramabouttheinformationwhichisavailable
withinitsdatabase.WhenaPrologprogramisloaded,wewillgetthequeryprompt,
?-'Itissunny'.
yes
?-
?-'Itiscold'.
no
?-
no
?-
?-’momoiscat'.
yes
?-
?-’momoisdog'.

12. Rules extend the logic program capabilities. Rules are used
to provide the decision-making process in Prolog. Rules are
specified in the form:
head:-t1,t2,t3,…..,tk.Wherek>=1
The head is known as the clause of the head.
:-isknownastheclauseneck.It
isreadas'if'.Thebodyofthe
clauseisspecifiedbyt1,t2,t3,…,
tk.Itcontainsoneormore
components,anditcanbe
separatedusingthecommas.A
rulewillreadas'headistrueif
t1,t2,t3,….,tkarealltrue'.
Rules
In the following program, first two lines indicate the facts and last two lines indicate the rules:
dog(pulu).large(pulu).
cat(momo).large(momo).
large_animal(A):-dog(A),large(A).
large_animal(C):-cat(C),large(C).
Theaboverulesmeanthat'large_animal(A)istrueifdog(A)istrue,andlarge(A)istrue,etc.'
Thelastlinemeansthat'large_animal(C)istrueifcat(C)istrue,andlarge(C)istrue.
Facts and Rules make up
the knowledge base.

13. likes(tarzan, jane).
likes(jane, tarzan).
likes(terk, jane).
facts
Arguments / objects / items
.dot is necessary to end the statement
relation
friends(X,Y):-likes(X,Y), likes(Y,X).
Predicate name
head body
variables
Horn Clause

14. Example
elephant(george).
elephant(mary).
elephant(X) :-grey(X), mammal(X), hasTrunk(X).
Procedure for elephant
Predicate
Clauses
Rule
Facts
?-elephant(george).
yes
?-elephant(jane).
no
Queries
Replies

15. Queries
Rules
facts
Example 1 :Belowfoodtable shows the facts, rules, goals and their English meanings.
Queries / Goals
?-food(pizza). // Is pizza a food?
?-meal(X), lunch(X). // Which food is meal and lunch?
?-dinner(sandwich). // Is sandwich a dinner?
Facts English meanings
food(burger). // burger is a food
food(sandwich). // sandwich is a food
food(pizza). // pizza is a food
lunch(sandwich). // sandwich is a lunch
dinner(pizza). // pizza is a dinner
Rule
meal(X) :-food(X).
// Every food is a meal OR
Anything is a meal if it is a food

16. Queries
Rules
facts
Example 2 :Below student-professor relation table shows the facts, rules, goals and their English meanings.
.
Facts English meanings
studies(charlie, csc135). // charlie studies csc135
studies(olivia, csc135). // oliviastudies csc135
studies(jack, csc131). // jack studies csc131
studies(arthur, csc134).
likes('John', car(bmw))
// arthur studies csc134
// Read as : john likes bmwcar
gives(john, chocolate, jane). // Read as : john gives chocolate to jane
Rules
professor(X, Y) :-
teaches(X, C),studies(Y, C).
// X is a professor of Y if X teaches
C and Y studies C.
Queries / Goals
?-studies(charlie, What).
// charlie studies what? OR
What does charlie study?
?-professor(kirke, Students).
// Who are the students of
professor kirke.

17. 19
ListsandSequenceinProlog
InProlog,thelistbuilderusesbrackets[...].Alistisreferredbythe
notation[A|B]inwhich,Aisthefirstelement,andwhosetailisB.
Thefollowingexampleshowsthethreedefinitions,wherethefirst
elementofthelistisrefereedbythe'car',thetailofthelistisreferred
by'cdr',listconstructorisreferredbythe'cons'.
car([A|B],A).
cdr([A|B],B).
cons[A,B,[A|S]).
Where,
•Aisthehead(car)of[A|B].
•Bisthetail(car)of[A|B].
•PutAattheheadandBasthetailconstructsthelist[A|S].
Thepredicate'member/2'definitionisdescribedasfollows:
member(A,[A|S]).
member(A,[B|S]):-member(A,S).
Theclausescanbereadasfollows:
•AisalistmemberwhosefirstelementisA.
•AisalistmemberwhosetailisSifAisamemberofS.

18. Theloopingfacilityiscontainedinmostoftheprogramming
languages.Loopingisusedtoenableasetofinstructionsto
berepeatedlyexecutedeitherafixednumberoftimesor
untilagivenconditionmet.Prologhasnoloopingfacility,
butwecanobtainasimilareffect.Usingthiseffect,wecan
evaluateasequenceofgoalsrepeatedly.Invariousways,
thiscanbedonelikebuilt-inpredicates,recursion,
backtracking,oracombinationofthese.
Intheaboveexample,wedefinethelooppredicatein
termsofitself.Thesecondclausereadas'toloopfromN,
firstwritetheN'svalue,thensubtractonetoprovideS,
thenloopfromM'.Thisprocesswillterminateusing
thefirstclause:'whentheargumentis0,thenstopordo
nothing'.Herethefirstclauseiscalledasterminated
condition.
Loopingafixednumberoftimes
Toexecutetheinstructionafixednumberoftimes,many
programminglanguagesprovide'forloop'.InProlog,there
isnosuchfacilityavailabledirectly,butusingrecursion,we
canobtainasimilareffect,whichisshowninthefollowing
programs:
LoopsinProlog
Example1:
Thisprogramoutputstheintegervaluefromaspecified
valuedownto1.
loop(0).
loop(N):-N>0,write('valueofNis:'),write(N),nl.
SisN-1,loop(S).
?-loop(4).
valueofNis:4
valueofNis:3
valueofNis:2
valueofNis:1
yes

19. Here are some simple clauses.
The following queries yield the specified answers.
How do you add the following facts?
likes(mary,food).
likes(mary,juice).
likes(john,juice).
likes(john,mary).
| ?-likes(mary,food).
yes.
| ?-likes(john,juice).
yes.
| ?-likes(john,food).
no.
John likes anything that Mary likes
John likes anyone who likes juice
John likes anyone who likes themselves
Example 3 :

20. Some Applications of Prolog
Prologisusedinvarious
domains.Itplaysavitalrolein
automationsystem.Following
aresomeotherimportant
fieldswherePrologisused−
Prologisusedinvarious
domains.Itplaysavitalrolein
automationsystem.Following
aresomeotherimportant
fieldswherePrologisused−
•IntelligentDatabaseRetrieval
•NaturalLanguageUnderstanding
•SpecificationLanguage
•MachineLearning
•RobotPlanning
•AutomationSystem
•Problem Solving
•Expert Systems
What is
Prolog used
for
Good at
▪Grammars and Language processing,
▪Knowledge representation and reasoning,
▪Unification,
▪Pattern matching,
▪Planning and Search.
i.e. Prolog is good at Symbolic AI.
?

21. 23
Advantages :
1.Easy to build database. Doesn’t
need a lot of programming effort
2.Pattern matching is easy.
Search is recursion based
.3.Ithasbuiltinlisthandling.
Makesiteasiertoplaywith
anyalgorithminvolvinglists.
2.Sometimes input and output is
not easy.
Disadvantages :
1.LISP(anotherlogic
programming language)
dominatesoverprologwith
respecttoI/Ofeatures
3. Repetitive number crunching,
Representing complex data
structures,
Input/output (interfaces).