A Heuristic Approach to Natural Language Processing

18 "1965 International Conference on Computational Linguistics" A Heuristic Approach to Natural Language Processing Denis M. Manelski and Shell Oil Company 50 West 50th Street New York 20, New York Gilbert K. I~l.ee Northwestern University Technological Institute Evanston, Illinois Manelskl & Krulee 1 ABSTRACT This paper is concerned with the design of a processor capable of formalizing English language descriptions of problems in the sententlal calculus. The emphasis is on the design of a system with natural language processing capabilities, but the formal languages specified are oriented to the problem context. A series of automata are specified to carry out the necessary functions. The automata identifythe premises in the problem strings~ specify the appropriate logical connectives among the premises and deter- mine which premises are meaning-equivalent. The syntax of each automaton is defined and examples are used to illustrate their functioning. The automata accept statements in the language L1, the set of English statements of problems in the sententlal calculus. The individual premises p @ L1 are recognized by the syntax~, where ~ is chosen so that the language L2 recognized by it is a subset of L1. Furthermore, the strings in L2 are restricted to the declarative sentences. Once the premises and their logical connectives have been identified, those that are meaning- equivalent are located in two additional steps. First the L2 description of the string is mapped into a string in L3. The L3 language consists of a limited set of canonical forms that ease the problem of establishing meaning equivalence of premises. Finally, the automaton applies heuristically a sequence of problem-orlented and meaning-preserving transformations in order to establish meaning-equivalence. Two premises are taken to be meaning-equivalent if one can be deduced from the other. Otherwise~ they are taken to be not meaning-equlvalent. Manelskl &Krulee 2 A HEURISTIC APPROACH TO NATURAL LANGUAGE PROCESSING 1 Introduction The recent evolution of programming languages has tended to improve communication between man and computer. The use of mnemonics~ automatic storage allocation~ English-like operators (such as in COBOL) and problem-oriented languages has greatly facilitated the task of the programmer. Thus, the solution algorithm for a large class of computa- tional problems can be defined with relative ease in languages such as FORTRAN and ALGOL, specifically designed for these classes of problems. This paper describes an attempt to further simplify the communica- tion between programmer and computer by defining a system which can produce a formal description from its natural (verbal) input. 2 In order to study this approach a specific problem area was chosen, the propositional or statement calculus. It will be evident that the problem area chosen has influenced the design of the system; nonetheless it should be clear that the linguistic capabilities of the system are general rather than specific to the problem context. In designing this processor, two major abilities are required. First, the processor must be able to identify each elementary premise and all logical connectives. It must also determine which premises are to be taken as equivalent. i …

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