Structure from Anarchy: Meta Level Representation of Expert System Propositions for Natural Language Interfaces.

Structure from Anarchy: Meta Level Representation of Expert System Propositions for Natural Language Interfaces. 1 Galina Datskovsky Moerdler Department of Computer Science Columbia University New York, N.Y. 10027 phone: (212) 280-8177 Arpanet: galina@ columbia.arpa.edu Abstract: In this paper we describe a meta level representation used for mapping natural language input into propositions of an expert system. This representation is based on verb classes that are structured hierarchically, with more general information encoded in the top level nodes and more specific information in the lower level nodes. Because of its structure, the representation is able to provide a detailed classification of the propositions, supplying a basis for defming semantics. It allows the system to answer questions about relationships between propositions without inferencing, as well as to answer questions the expert system could not previously handle. 1 Introduction A great deal of work has been done in constructing natural language interfaces to well structured underlying systems, such as data base systems. These natural language interfaces generally make use of an assumed system structure, such as a schema, to define semantics [Martin, Appelt and Pereira 83; Grosz et. al. 85] [Woods et. al. 72; Woods 73] [Kaplan 79]. On the other hand, almost no effort has been made in constructing natural language interfaces to systems that do not have such an extensive description, e.g. expert systems 2. The lack of such a schema means that the~ is no easy way to obtain information about propositions 3 of the underlying system. Thus, in order to build a natural 2Throughout thlt paper we •m only ooncemed with expert systems that must communicate with their uteri in ot'der to gather data befon~ giving advice, inch It Mycin [Shot~liffe 76] 3In the rule of the form IF A and B them C, A, B and C an~ propositions. The terms pmlxmtion and fact an~ used interch~geably throughout thl. paper. language interface to expert systems the semantic interpreter must be able to provide the necessary structure. In an earlier paper [Datskovsky Moerdler eLal. 87] we briefly described a semantic interpreter that maps user statements into facts of an expert system, as well an inference engine for expert systems that can efficiendy utilize this input. In this paper we discuss the meta level description of the expert system propositions, similar to a schema of a data base, utilized by the semantic interpreter and show how this structure is used in processing of user questions. Our structure consists of a group of hierarchies which are formed from verb categories. The hierarchies provide a grouping of the propositions of an expert system by topic. For example, all propositions that deal with interpersonal relationships are grouped under one hierarchy, while those dealing with transfer of possession are grouped under another. The meaning of a proposition is specified step by step, as the hierarchy is traversed, thus allowing for mapping of various sentences, or parts of sentences into the propositions. To test our theories, the approach is currendy being implemented as a front …

Content truncated to 500 words