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CS 603: Programming Languages

CS 603: Programming Languages. Lecture 29 Spring 2004 Department of Computer Science University of Alabama Joel Jones. Overview. More about Definite Clause Grammars Extra Goals Building parse trees Using Horn Clauses as a denotational semantics. Even More on Definite Clause Grammars.

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CS 603: Programming Languages

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  1. CS 603: Programming Languages • Lecture 29 • Spring 2004 • Department of Computer Science • University of Alabama • Joel Jones

  2. Overview • More about Definite Clause Grammars • Extra Goals • Building parse trees • Using Horn Clauses as a denotational semantics

  3. Even More on Definite Clause Grammars • Taken from: • http://www.coli.uni-sb.de/~kris/prolog-course/html/node69.html • Using Peano numbers seems a little extreme, can’t we use numbers? • Yes, remember N1 is N + 1 ? • Since DCGs are really syntactic sugar for ordinary Prolog rules, why not have syntactic sugar in DCGs for ordinary rules?

  4. Sugar for DCGs s(Count) --> ablock(Count), bblock(Count), cblock(Count). ablock(0) --> []. ablock(NewCount) --> [a],ablock(Count), {NewCount is Count + 1}. bblock(0) --> []. bblock(NewCount) --> [b],bblock(Count), {NewCount is Count + 1}. cblock(0) --> []. cblock(NewCount) --> [c],cblock(Count), {NewCount is Count + 1}.

  5. Using Ordinary Rules in DCGs for Attributes • Last time, we used arguments to carry information about the role the pronoun was playing in a particular rule: • s --> np(subject),vp. np(_) --> det,n.np(X) --> pro(X).vp --> v,np(object).pro(subject) --> [he]. • But what if we need pronouns to have more than one attribute?

  6. Separate Rules and Lexicons • What? Eliminate all mention of individual words in DCGs and record all information about words separately Lexicon: Original: lex(the,det). lex(a,det). lex(woman,n). lex(man,n). lex(shoots,v). np --> det,n. vp --> v,np. vp --> v. det --> [the]. det --> [a]. n --> [woman]. n --> [man]. v --> [shoots].   Becomes: Changed rules: det --> [Word],{lex(Word,det)}. n --> [Word],{lex(Word,n)}. v --> [Word],{lex(Word,v)}.

  7. Using Horn Logic as a Semantic System • This discussion is taken from: • http://www.cs.nmsu.edu/~gupta/logden/lnai.ps • Why another semantics specification technique? • More program-like, executable • Ease parallel translation

  8. Logical Denotations • Denotational Semantics consist of: • syntax: context free grammar • semantic algebra: basic domains along with operations over those domains • valuation functions: mappings from patterns of parse trees to values in the domains of the semantic algebra

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