© Patrick Blackburn, Johan Bos & Kristina Striegnitz Logic Programming About the course –Taught in English –Tuesday: mostly theory –Thursday: practical.

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© Patrick Blackburn, Johan Bos & Kristina Striegnitz Logic Programming About the course –Taught in English –Tuesday: mostly theory –Thursday: practical work [lab] Teaching material –Learn Prolog Now! –SWI Prolog interpreter

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Learn Prolog Now!

© Patrick Blackburn, Johan Bos & Kristina Striegnitz SWI Prolog Freely available Prolog interpreter Works with –Linux, –Windows, or –Mac OS There are many more Prolog interpreters Not all are ISO compliant

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Lecture 1 Theory –Introduction to Prolog –Facts, Rules and Queries –Prolog Syntax Exercises –Exercises of LPN chapter 1 –Practical work

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Aim of this lecture Give some simple examples of Prolog programs Discuss the three basic constructs in Prolog: –Facts –Rules –Queries Introduce other concepts, such as –the role of logic –unification with the help of variables Begin the systematic study of Prolog by defining terms, atoms, and variables

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Prolog "Programming with Logic" Declarative Very different from other (procedural) programming languages Good for knowledge-rich tasks

© Patrick Blackburn, Johan Bos & Kristina Striegnitz History of Prolog s/1990s 2005 first Prolog interpreter by Colmerauer and Roussel

© Patrick Blackburn, Johan Bos & Kristina Striegnitz History of Prolog s/1990s 2005 implementation of DEC10 compiler by Warren

© Patrick Blackburn, Johan Bos & Kristina Striegnitz History of Prolog s/1990s 2005 Definite Clause Grammars implementation by Pereira and Warren

© Patrick Blackburn, Johan Bos & Kristina Striegnitz History of Prolog s/1990s 2005 Prolog grows in popularity especially in Europe and Japan

© Patrick Blackburn, Johan Bos & Kristina Striegnitz History of Prolog s/1990s 2005 Prolog used to program natural language interface in International Space Station by NASA

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Basic idea of Prolog Describe the situation of interest Ask a question Prolog logically deduces new facts about the situation we described Prolog gives us its deductions back as answers

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Consequences Think declaratively, not procedurally –Challenging –Requires a different mindset High-level language –Not as efficient as, say, C –Good for rapid prototyping –Useful in many AI applications

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party.

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- woman(mia).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- woman(mia). yes ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- woman(mia). yes ?- playsAirGuitar(jody).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- woman(mia). yes ?- playsAirGuitar(jody). yes ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- woman(mia). yes ?- playsAirGuitar(jody). yes ?- playsAirGuitar(mia). no

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- tattoed(jody).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- tattoed(jody). no ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- tattoed(jody). ERROR: predicate tattoed/1 not defined. ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- party.

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- party. yes ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- rockConcert.

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 1 woman(mia). woman(jody). woman(yolanda). playsAirGuitar(jody). party. ?- rockConcert. no ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). fact

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). fact

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). fact rule

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). fact rule

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). fact rule

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). headbody

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). ?- playsAirGuitar(mia). yes ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 2 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). ?- playsAirGuitar(mia). yes ?- playsAirGuitar(yolanda). yes

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Clauses happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). There are five clauses in this knowledge base: two facts, and three rules. The end of a clause is marked with a full stop.

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Predicates happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda). There are three predicates in this knowledge base: happy, listens2music, and playsAirGuitar

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 3 happy(vincent). listens2music(butch). playsAirGuitar(vincent):- listens2music(vincent), happy(vincent). playsAirGuitar(butch):- happy(butch). playsAirGuitar(butch):- listens2music(butch).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Expressing Conjunction happy(vincent). listens2music(butch). playsAirGuitar(vincent):- listens2music(vincent), happy(vincent). playsAirGuitar(butch):- happy(butch). playsAirGuitar(butch):- listens2music(butch). The comma “," expresses conjunction in Prolog

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 3 happy(vincent). listens2music(butch). playsAirGuitar(vincent):- listens2music(vincent), happy(vincent). playsAirGuitar(butch):- happy(butch). playsAirGuitar(butch):- listens2music(butch). ?- playsAirGuitar(vincent). no ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 3 happy(vincent). listens2music(butch). playsAirGuitar(vincent):- listens2music(vincent), happy(vincent). playsAirGuitar(butch):- happy(butch). playsAirGuitar(butch):- listens2music(butch). ?- playsAirGuitar(butch). yes ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Expressing Disjunction happy(vincent). listens2music(butch). playsAirGuitar(vincent):- listens2music(vincent), happy(vincent). playsAirGuitar(butch):- happy(butch). playsAirGuitar(butch):- listens2music(butch). happy(vincent). listens2music(butch). playsAirGuitar(vincent):- listens2music(vincent), happy(vincent). playsAirGuitar(butch):- happy(butch); listens2music(butch).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Prolog and Logic Clearly Prolog has something to do with logic Operators –Implication :- –Conjunction, –Disjunction ; Use of modus ponens Negation

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 4 woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Prolog Variables woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- woman(X).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Variable Instantiation woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- woman(X). X=mia

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Asking Alternatives woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- woman(X). X=mia;

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Asking Alternatives woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- woman(X). X=mia; X=jody

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Asking Alternatives woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- woman(X). X=mia; X=jody; X=yolanda

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Asking Alternatives woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- woman(X). X=mia; X=jody; X=yolanda; no

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 4 woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- loves(marsellus,X), woman(X).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 4 woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- loves(marsellus,X), woman(X). X=mia yes ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 4 woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- loves(pumpkin,X), woman(X).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 4 woman(mia). woman(jody). woman(yolanda). loves(vincent, mia). loves(marsellus, mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). ?- loves(pumpkin,X), woman(X). no ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 5 loves(vincent,mia). loves(marsellus,mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). jealous(X,Y):- loves(X,Z), loves(Y,Z).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 5 loves(vincent,mia). loves(marsellus,mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). jealous(X,Y):- loves(X,Z), loves(Y,Z). ?- jealous(marsellus,W).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Knowledge Base 5 loves(vincent,mia). loves(marsellus,mia). loves(pumpkin, honey_bunny). loves(honey_bunny, pumpkin). jealous(X,Y):- loves(X,Z), loves(Y,Z). ?- jealous(marsellus,W). W=vincent ?-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Prolog Syntax What exactly are facts, rules and queries built out of? Terms Simple TermsComplex Terms ConstantsVariables AtomsNumbers Terms Simple TermsComplex Terms ConstantsVariables AtomsNumbers

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Atoms A sequence of characters of upper-case letters, lower-case letters, digits, or underscore, starting with a lowercase letter Examples: butch, big_kahuna_burger, playGuitar An arbitrary sequence of characters enclosed in single quotes Examples: 'Vincent', 'Five dollar shake', A sequence of special characters Examples: :, ;. :-

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Numbers Integers: 12, -34, Floats:

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Variables A sequence of characters of uppercase letters, lower-case letters, digits, or underscore, starting with either an uppercase letter or an underscore Examples: X, Y, Variable, Vincent, _tag

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Complex Terms Atoms, numbers and variables are building blocks for complex terms Complex terms are built out of a functor directly followed by a sequence of arguments Arguments are put in round brackets, separated by commas The functor must be an atom

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Examples of complex terms Examples we have seen before: –playsAirGuitar(jody) –loves(vincent, mia) –jealous(marsellus, W) Complex terms inside complex terms: –hide(X,father(father(father(butch))))

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Arity The number of arguments a complex term has is called its arity Examples: woman(mia) is a term with arity 1 loves(vincent,mia) has arity 2 father(father(butch)) arity 1

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Arity is important In Prolog you can define two predicates with the same functor but with different arity Prolog would treat this as two different predicates In Prolog documentation arity of a predicate is usually indicated with the suffix "/" followed by a number to indicate the arity

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Example of Arity This knowledge base defines –happy/1 –listens2music/1 –playsAirGuitar/1 happy(yolanda). listens2music(mia). listens2music(yolanda):- happy(yolanda). playsAirGuitar(mia):- listens2music(mia). playsAirGuitar(yolanda):- listens2music(yolanda).

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Exercises

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Summary of this lecture Simple examples of Prolog programs Introduced three basic constructs in Prolog: –Facts –Rules –Queries Discussed other concepts, such as –the role of logic –unification with the help of variables Definition of Prolog constructs: terms, atoms, and variables

© Patrick Blackburn, Johan Bos & Kristina Striegnitz Next lecture Discuss unification in Prolog Prolog's search strategy