October 2004csa4050: Semantics V1 CSA4050: Advanced Topics in NLP Semantics V NL Access to Databases Semantics of Questions and Answers Simple Interpreters for Questions

October 2004csa4050: Semantics V2 Access to Databases: 3 approaches DB Query Language Form Interface Natural Language

October 2004csa4050: Semantics V3 DB Query Language range of C is countries range of Cont is continents range of I is inclusions retrieve( Cont.name, count(C.name where C.name = I.inside and I.outside = Cont.name))

October 2004csa4050: Semantics V4 Form Interface

October 2004csa4050: Semantics V5 Natural Language How many countries are there in each continent?

October 2004csa4050: Semantics V6 Issues Accessibility –Type of query language –What needs to be learned to make a query? –Data input vs. data output Flexibility –Can types of question be predicted? –Can types of question be easily changed? Expressivity –Limitations on kinds of information present –What types of query is possible

October 2004csa4050: Semantics V7 Chat 80 Pereira and Warren (1983) General Architecture ENGLISH LOGICAL FORM PROLOG ANSWER Translation: what does the question mean Planning: how shall I answer it Execution: what is the answer?

October 2004csa4050: Semantics V8 Different Types of Sentence Sentence TypeCommunicative Act Declarative SentenceAssertion Interrogative SentenceQuestion Imperative SentenceCommand

October 2004csa4050: Semantics V9 Sentences and Assertions Assertions are usually expressed by declarative sentences. Our grammar/lexicon deals with very simple examples, e.g. John saw Fido More complex declarative sentences include All candidates for CSA4050 failed. Candidates who fail more than four credits shall not be allowed to take resits.

October 2004csa4050: Semantics V10 Sentences and Questions Questions are usually expressed by interrogative sentences. Our simple grammar/lexicon does not yet deal with interrogative sentences. To handle them we must modify the grammar Issue: how do we recognise interrogative sentences?

October 2004csa4050: Semantics V11 Execution of Communicative Acts Assertions add information to the database. The meaning of a declarative sentence involves execution an appropriate assert operation Questions query information in the database. The meaning of an interrogative sentence involves execution of an appropriate query operation Commands identify actions to be carried out.

October 2004csa4050: Semantics V12 Assertions and Questions: Semantic Representation SentenceRepresentation of Semantic Content Representation of Communicative Act John sees Fido see(john,fido)a1(see(john,fido)) Does John see Fido see(john,fido)q1(see(john,fido))

October 2004csa4050: Semantics V13 Basic Processing process(Sent,Result) :- s(SEM,Sent,[]), interpret(SEM,Result). In other words: to process the sentence: Parse it to produce semantic representation SEM Interpret SEM and give back RESULT Next we must define the interpret predicate

October 2004csa4050: Semantics V14 Defining the Interpreter interpret(a1(X),A) :- a1(X,A). interpret(q1(Q),A) :- q1(Q,A).

October 2004csa4050: Semantics V15 Very Basic Intepretation a1(SEM,ok) :- asserta(SEM). In the case of an assertion, just assert it. N.B. no check for previous assertion. q1(SEM,yes) :- call(SEM), !. q1(SEM,no). If it’s a yes-no question, see if it’s true

October 2004csa4050: Semantics V16 Dealing with Syntax We now have a primitive interpretation mechanism in place. It remains to modify the grammar/lexicon to handle the syntax of these very simple questions. To begin with, we will limit ourselves to yes/no questions

October 2004csa4050: Semantics V17 Yes/No Questions: Grammar Rules for S % Declarative sentence s --> np, vp. John sees Fido % interrogative sentence s --> aux, np, vp. does John see Fido ?

October 2004csa4050: Semantics V18 S Rule with Arguments :- [process]. s(a1(S)) --> np(VP^S), vp(VP). s(q1(S)) --> aux, np(VP^S), vp(VP).

October 2004csa4050: Semantics V19 Complete Grammar s(a1(S)) --> np(VP^S), vp(VP). s(q1(S)) --> aux, np(VP^S), vp(VP). np(NP) --> n(NP). np(NP) --> d(N^NP), n(N). vp(VP) --> v(VP). vp(Z^P) --> v(V2), np(NP), {reduce(V2,Z,V1), reduce(NP,V1,P)}. % lexicon aux --> [does]. aux --> [did]. v(X^walk(X)) --> [walk]. v(X^walk(X)) --> [walked]. v(X^Y^chased(X,Y)) --> [chase]. v(X^Y^chased(X,Y)) --> [chased]. n(X^cat(X)) --> [cat]. n(VP^S) --> [suzie], {reduce(VP,suzie,S)}. n(VP^S) --> [felix], {reduce(VP,felix,S)}. d(RL^SL^some(X,R,S)) --> [a], {reduce(RL,X,R),reduce(SL,X,S) }.

October 2004csa4050: Semantics V20 Demo ?- process([does,john,see,fido],A). A=no ?- process([john,sees,fido],A). A=ok ?- process([does,john,sees,fido],A). A=yes

October 2004csa4050: Semantics V21 Improving the Interpreter dbq :- readLine(L), dbq1(L), !, dbq. dbq1([halt]) :- nl, write(bye), !, fail. dbq1(Sent) :- process(Sent,A).