PROLOG language

Introduction

Alogicprogramminglanguage.In1972,inordertoimprovetheexecutionefficiencyoftheresolutionmethod,theFrenchComorauerteamdevelopedaprogramexecutorforthetheoremprovingprogram,namedPROLOG(ProgrammingInLogic),markingthebirthofthefirstlogicprogramminglanguagePROLOG.In1974andafter,R.KowalskifurtherclarifiedthetheoreticalbasisofPROLOGfromtheperspectiveoftheHORNclauseofpredicatelogic,andsystematicallyproposedtheideaof​​logicalprogramming.

TherearethreetypesofbasicsentencesinPROLOGlanguage,whichrepresentfacts,rules,andqueries,andcorrespondtotheHORNclauseswithhead(withoutbody,body)andheadless.Forexample:

SotheprogramminginPROLOGlanguagecanbeboileddowntodeclaringfacts,definingrulesandaskingquestions.

TheexplanationandexecutionprocessofthePROLOGprogramusesaspecificinputresolution,thatis,startingfromthetargetsentence,findtheresolution(tailandheadmatching)ofaclauseintheoriginalclauseset,andthenewclauseThenfindtheresolutionwithaclauseintheoriginalclauseset,andsoon.Atanytime,noresolutionisfoundbetweentwoderivedclausesortwoclausesoftheoriginalclauseset.Intheaboveexample

⑥:-human(u),greek(u)(theresolutionof④and⑤,mgu=u/x)

⑦:-greek(socarates)(Theresolutionof②and⑥,mgu=socarates/u)

⑧:-(Theresolutionof③and⑦,getemptyclauses)

Theanswertothequestionisu=socarates.ItcanbeseenthatthePROLOGinterpretationsystemisactuallyatheoremprovingprogramorproblemsolvingprogrambasedontheresolutionprinciple.

Lowspace-timeefficiencyisanimportantissuethataffectstheapplicationofthePROLOGlanguage.Thewaystoimproveefficiencyare:improvethePROLOGinterpretationsystem,adoptthePROLOGcompilationsystem,developthePROLOGmachine,introducethemeta-rulesforcontrol,anduseheuristicsSearchmode,enableintelligentbacktracking,adoptcollaborativeandconcurrentsolvingtechnology,anddevelopparallelprocessingmechanisms.

BecausethePROLOGinterpretercanautomaticallyfindthesolutionoftheproblemaccordingtotheinferencerules,theprogrammercanfocusonrevealingthelogicalrelationshipbetweentheobjectswithouthavingtoconsiderthedetailsoftheprocesstoomuch.Astepforwardinthedirectionofautomaticprogramming.ButPROLOGlanguagealsohassomenon-logicalcharacteristics.Forexample,inordertocontrolthebacktracking,theCUTtechnology(cuttingtechnology,whichmeansthattheprogrampersonnelusetheCUTsymbol!Informsthesystemtonolongerconsidertheuselesssearchpaththathasbeencarriedoutinthepastandthereisnoneedtorecordthetechnologyofthebacktrackingpoint),andintroducethepredicateassert(inthedatabaseAddclause)retract(deleteclausefromthedatabase).Thismakesthesetofaxiomsofthesystemchangeintheprocessofreasoning,whichareinconsistentwiththebasicideasofthesameorderoflogic.Therefore,PROLOGisnotalogicalprogramminglanguageinthestrictsense.Inordertomakeitmorelogical,itisnecessarytolimitthenon-logicalcomponentsoflanguagetoaminimum.Researchinthisareaisongoing.

Bibliography

W.F.ClocksinandC.S.Mellish,ProgramminginProlog,Springer-Verlag,Berlin,1981.