Auszug aus: Künstliche Intelligenz, Heft 2/2009, ISSN 0933-1875, BöttcherIT Verlag, Bremen, www.kuenstliche-intelligenz.de/order Polymorphism as a Model for Ambiguity: the Case of Nominal Modification Walid S. Saba We suggest modeling concepts as types in a strongly-typed ontology that reflects our commonsense view of the world and the way we talk about it in ordinary language. In such a framework, certain types of ambiguities in natural language are explained by the notion of polymorphism. In this paper we suggest such a typed compositional semantics for nominal compounds of the form (Adj Noun) where adjectives are modeled as higher-order polymorphic functions. In addition to (Adj Noun) compounds our proposal seems also to suggest a plausible explanation for well known adjective ordering restrictions. 1 Introduction Over two decades ago a "quite revolution", as Charniak (1995) once called it, overwhelmingly replaced knowledge- based approaches in natural language processing (NLP) by quantitative (e.g., statistical, corpus-based, machine learn- ing) methods. In recent years, however, the terms ontology, semantic web and semantic computing have been in vogue, and regardless of how these terms are being used (or misused) we believe that this ’semantic counter revolution’ is a positive trend since corpus-based approaches to NLP, while useful in some language processing tasks - see (Ng and Zelle, 1997) for a good review - cannot account for compositionality and productivity in natural language, not to mention the complex inferential patterns that occur in ordinary language use. The inferences we have in mind here can be illustrated by the following example: (1) Pass that car will you. ฀a) He is really annoying me. ฀b) T hey are really annoying me. Clearly, speakers of ordinary language can easily infer that ’he’ in (1a) refers to the person driving [that] car, while ’they’ in (1b) is a reference to the people riding [that] car. Such inferences, we believe, cannot theoretically be learned (how many such examples will be needed, and what exactly would constitute a negative example in this context?), and are thus beyond the capabilities of any quantitative approach. On the other hand, and although it is our firm belief that purely quantitative approaches cannot be the only paradigm for NLP, dissatisfaction with purely engineering approaches to the construction of large knowledge bases for NLP (e.g., Lenat and Ghua, 1990) are somewhat justified. While lan- guage ’understanding’ is, for the most part, a commonsense ’reasoning’ process at the pragmatic level, as example (1) il- lustrates, the knowledge structures that an NLP system must utilize should have sound linguistic and ontological under- pinnings and must be formalized if we ever hope to build scalable systems (or, as John McCarthy once said, if we ever hope to build systems that we can actually understand!). As we have argued elsewhere (Saba, 2007), therefore, we believe that both trends are partly misguided and that the time has come to enrich logical semantics with an ontological struc- ture that reflects our commonsense view of the world and the way we talk about in ordinary language. Specifically, we argue that very little progress within logical semantics have been made in the past several years due to the fact that these systems are, for the most part, mere symbol manipula- tion systems that are devoid of any content. What we suggest instead is a semantics that is grounded in a strongly-typed ontology - an ontology that reflects our commonsense view of reality and the way we talk about it in ordinary language. In this paper we suggest exactly such a semantics and we subsequently demonstrate the utility of this approach by tackling one particular challenge in the semantics of natu- ral language. Specifically, in this paper we will first introduce the notions of intersective vs. non-intersective adjectives, as well as the notion of adjective-ordering restrictions. In sec- tion 2 we will introduce a strongly typed system that re- flects our commonsense view of the world and the way we talk about it in ordinary spoken language. In the rest of the paper we will suggest how such a strongly-typed composi- tional system can possibly utilize such information to explain the adjective-ordering restriction phenomenon as well as the type of ambiguity that occurs in nominal modification. 2 Ambiguity in Nominal Modification The ambiguity in nominal modification we are concerned with here can be illustrated by the sentence in (2), which could be uttered by someone who believes that: (i) Olga is a dancer and a beautiful person; or (ii) Olga is beautiful as a dancer (i.e., Olga is a dancer and she dances beautifully). (2) Olga is a beautiful dancer. As suggested by Larson (1998), there are two possible routes to explain this ambiguity: one could assume that a noun such as dancer is a simple one place predicate of type e, t and ’blame’ this ambiguity on the adjective; alterna- KI 2/09 18 Fachbeitrag