tailieunhanh - Báo cáo khoa học: "ISSUES IN NATURAL LANGUAGE ACCESS TO DATABASES FROM A LOGIC PROGRAMMING PERSPECTIVE"

I shall discuss issues in natural language (NL) access to databases in the light of an experimental NL questlon-answering system, Chat, which I wrote with Fernando Perelra at Edinburgh University, and which is described more fully elsewhere [8] [6] [5]. Our approach was strongly influenced by the work of Alaln Colmerauer [2] and Veronica Dahl [3] at Marseille University. Chat stages: processes a NL question in three main relational database system. | ISSUES IN NATURAL LANGUAGE ACCESS TO DATABASES FROM A LOGIC PROGRAMMING PERSPECTIVE David H D Warren Artificial Intelligence Center SRI International Menlo Park CA 94025 USA I INTRODUCTION I shall discuss Issues In natural language NL access to databases In the light of an experimental NL question-answering system Chat which I wrote with Fernando Pereira at Edinburgh University and which Is described more fully elsewhere 8 6 5 . Our approach was strongly Influenced by the work of Alain Colmerauer 2 and Veronica Dahl 3 at Marseille University. Chat processes a NL question in three main stages translation planning execution J English ---- logic ---- Prolog ----- answer corresponding roughly to What does the question mean How shall I answer It What is the answer . The meaning of a NL question and the database of Information about the application domain are both represented as statements In an extension of a subset of first-order logic which we call definite closed world DCW logic. This logic is a subset of first-order logic In that It admits only definite statements uncertain information Either this or that Is not allowed. DCW logic extends first-order logic In that it provides constructions to support the closed world assumption that everything not known to be true is false. Why does Chat use this curious logic as a meaning representation language The main reason Is that it can be Implemented very efficiently. In fact DCW logic forms the basis of a general purpose programming language Prolog 9 1 due to Colmerauer which has had a wide variety of applications. Prolog can be viewed either as an extension of pure Lisp or as an extension of a relational database query language. Moreover the efficiency of the DEC-10 Prolog implementation is comparable both with compiled Lisp 9 and with current relational database systems 6 for databases within virtual memory . Chat s second main stage planning Is responsible for transforming the logical form of the NL query Into efficient