Advanced Topics in NLP

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Advanced Topics in NLP

• Semantics V
• NL Access to Databases
• Semantics of Questions and Answers
• Simple Interpreters for Questions

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Access to Databases3 Approaches

• Natural Language
• DB Query Language
• Form Interface

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Natural Language

• How many countries are there in each continent?
• What is their average population?

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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))

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Form Interface
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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

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Chat 80 Pereira and Warren (1983)General
Architecture
Translation what does the question mean
Planning how shall I answer it
Execution what is the answer?
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Different Types of Sentence
Sentence Type Communicative Act
Declarative Sentence Assertion
Interrogative Sentence Question
Imperative Sentence Command
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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 includeAll
  candidates for CSA4050 failed.Candidates who
  fail more than four credits shall not be allowed
  to take resits.

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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?

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Execution ofCommunicative 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.
• Representation of communicative act is in
  addition to representation of content.

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Assertions and Questions Semantic Representation
Sentence Representation 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))
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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

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Defining the Interpreter

• interpret(a1(X),A) -
• a1(X,A).
• interpret(q1(Q),A) -
• q1(Q,A).

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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 its a yes-no question, see if its true

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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

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Yes/No QuestionsGrammar Rules for S

• Declarative sentence
• s --gt np, vp.
• John sees Fido
• interrogative sentence
• s --gt aux, np, vp.
• does John see Fido ?

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S Rule with Arguments

• - process.
• s(a1(S)) --gt
• np(NP), vp(NP),
• reduce(VP,NP,S).
• s(q1(S)) --gt
• aux, np(NP), vp(VP),
• reduce(VP,NP,S).

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Demo

• ?- process(does,john,see,fido,A).
• Ano
• ?- process(john,sees,fido,A).
• Aok
• ?- process(does,john,sees,fido,A).
• Ayes

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Improving the Interpreter

• dbq -
• readLine(L),
• dbq1(L),
• !,
• dbq.
• dbq.
• dbq1(halt) - nl, write(bye), !, fail.
• dbq1(Sent) - process(Sent,A).