Semantic Information Preprocessing for Natural Language Interfaces to Databases

Semantic Information Preprocessing for Natural Language Interfaces to Databases Milan Mosny Simon Fraser University Burnaby, BC VhA 1S6, Canada mosny@cs.sfu.ca Abstract An approach is described for supplying se- lectional restrictions to parsers in natural language interfaces (NLIs) to databases by extracting the selectional restrictions from semantic descriptions of those NLIs. Au- tomating the process of finding selectional restrictions reduces NLI development time and may avoid errors introduced by hand- coding selectional restrictions. 1 Introduction An approach is described for supplying selectional restrictions to parsers in natural language interfaces (NLIs) to databases. The work is based on Linguis- tic Domain Theories (LDTs) (Rayner, 1993). In our approach, we propose a restricted version of LDTs (RLDTs), that can be normalized and in normal- ized form used to construct selectional restrictions. We assume that semantic description of NLIs is de- scribed by such an RLDT. The outline of the paper is as follows. Section 2 provides a brief summary of original LDTs, il- lustrates how Abductive Equivalential Translation (AET) (Rayner, 1993) can use them at run-time, and describes RLDTs. Sections 3 and 4 describe off- line processes - the normalization process and the extraction of selectional restrictions from normalized RLDTs respectively. Section 5 contains discussion, including related and future work. 2 LDT, AET and RLDT LDT and AET. LDT was introduced for a sys- tem, where input is a logical formula, whose predi- cates approximately correspond to the content words of the input utterance in natural language (lexical predicates). Output is a logical formula, consist- ing of predicates meaningful to the database engine (database predicates). AET provides a formalism for describing how a formula consisting of lexical predicates can be tranlsated into formula consisting of database predicates. The information used in the translation process is an LDT. A theory r contains horn clauses v(p~ A... A P,, --* Q) or universal conditional equivalences v(P1 ^... ^ P. ~ (RI ^... ^ Rz -= F)) or existential equivalences V((3Xl.- .Xm.P) -- F) where Pi, Ri denote atomic formulas, Q denotes a literal, F denotes a formula and V denotes universal closure. The LDT also contains functional relation- ships that are used for simplifications of the trans- lated formulas and assumption declarations. Given a formula Fting consisting of lexical predicates and an LDT, AET tries to find a set of permissible assump- tions A and a formula Fab consisting of the database predicates such that F u A =~ V(Fti,g = Fab) The translation of Fzi,g is done one predicate at a time. For each predicate in the formula Fting, there is a so-called conjunctive context that consists of conjuncts occurring together with the predicate in Fting, meaning postulates in the theory P, and the information stored in the database. Given an LDT, this conjunctive context determines how the predi- cate will be translated by AET. As an example, suppose that the lexical represen- tation of the sentence Is there a student who takes cmpt710 or cmpt7207 is Fzin~: :iX, E, Y, Y1 .student(X) A …

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