Collative Semantics

Collative Semantics Dan Fass Computing Research Laboratory New Mexico State University Las Cruces, NM, USA 88003 O. Abstract This paper introduces Collativc Semantics (CS), a new domain-independent semantics for n~tural language processing (NLP) which addresses the problems of lexieal ambiguity, met(> nymy, various semantic relations (conventional relations, redundant relations, contradictory relations, metaphorical rela- tions and severely anomalous relations) aud the introduction of new information. We explain the two techniques CS uses for matching together knowledge structures (KSs) and why seman- tic vectors, which record the results of such matches, arc infor- mative enough to tell apart semantic relations and be tile basis for lcxical disa.mbiguation. 1. Introduction Collative Semantics is a new domain-independent sem,~n- tics for NI,P. This paper foeusses on CS, describing tile main issues it addresses (lexical ambiguity, mctonymy, semantic rela- tions, introduction of new information) and general details of its knowledge representation, knowledge structures, techniques for matching together knowledge structures, and the way it records the results of matching in semantic vectors. CS has l)een implemented in a natural language program eaiicd recta5 which has been described in detail clsewherc (Fass, 1986). Briefly, the program produces semantic representations of single sentences requiring lexical disambiguation and met(> nymic infereneing. While processing such sentences recta5 com- putes semantic vectors for the matches between pairs of word- senses which are rich enough to discriminate between instances of conventional relations, semantically redundant relations, con- tradictory relations, metaphoricM relations and severely anomalous relations between word-sense pairs. Semantic vectors also record the assertion of new information. Meta5 can process all the example sentences given in the next section. 2. Semantic Relations, Novel Information and Meto- nymy In this section we provide brief descriptions of those semantic phcnomcna considered by CS, except lexical ambiguity, starting with semantic relations. Conventional, metaphorical and severely anomalous relations can all be described using the terminology of Richards (1936). The subject term is the "topic," the term it is compared to is the "vehicle," the similarity or resemblance between them is the "ground," and any difference or dissimilarity is tile "tension." We also adopt Perrine's (1971) four-fold classification of metaphors into combinations of explicit and implicit topics and vehicles. In a metaphorical relation there is tension between the topic and vehicle because the topic term is not a type of vehicle term. What is salient (Ortony, 1979) is given by the context, a salient property of the vehicle is found and an analogical match discovered between it and u property from the topic. The remaining properties of the topic and vehicle have similarities and differences and, although these are not central to recognis- ing the metaphorical relation, the higher the proportion of differences to similarities the "better" the metaphor. For example, in the metaphorical relation between 'cal" and 'drink' ill (1) "The car drank gasoline." the topic is 'ear' and the implicit vehicle is 'animal', the agent preference Wilks, 1975) of 'drink'. The tension is caused by a car (the topic) not being a type of animal (the vehicle). …

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