Adjectival Modification in Text Meaning Representation

Tiffs work belongs to a family of research efforts, called nficrotheories and aimed at describing the static inemfing of all lexical categories in several languages in the fr,'unework of tile MikroKosmos project on computational semantics. The latter also involves other static microtheories describing world kalowledge and syntax-semantics mapping as well as dynamic microtheories comlected with the actual process of text analysis. Tiffs paper describes our approach to detecting ,'rod recording adjectival meaning, compares it with the body of kalowledge on adjectives in literature and presents a detailed, practically tested methodology for the acquisition of lexical entries for adjecfives. The work was based on the set of over 6,000 English and about 1,500 Spanish adjectives obtained from task-oriented corpora. 1. The Ontological Approach The work on adjectives reported in tlfis paper constitutes a descriptive "microtheory" in the MikroKosmos semantic analyzer (Onyshkevych and Nirenburg 1994; and Beale et ,'d. 1995), designed to serve as a component of a lolowledge-based machine translation system (Nircnburg ct al. 1992). MikroKosmos combines findings from a variety of quasi-antonomous microtheories of language phenomena, world knowledge organization and procedural knowledge at the level of coinputer system arclfitectnrc. The basic motivation for this organization is the continued inability of the fields of lingnistics and NLP to produce a general-coverage, unified theory of trealment of language phenomena, a failure especially pronoanced in ,areas beyond computational syntax. The purpose and result of the MikroKosmos mmlysis process is the derivation of an interlingnal representation for natm'al language inlmts. The langtmge in which these representations arc expressed is called file "text meaning representation" (I'MR) langlmge, mid "texts" in dais language are called, simply, TMRs. TMR is a fr,'une-based language, where frame names typically re fe r to instances of ontological concepts, slot names are derived from a set of ontological properties and slot fillers ,are either elements of property value sets or pointers to concept instances. An ontology, a world model containing ilfformation about types of things, events mid properties in the world, is a necessary prerequisite for a TMR language. "An ontology for NLP purposes is a body of knowledge about the world (or a domain) that a) is a repository of primitive symbols used in meaning representation; b) organizes these symbols in a tangled subsumption hierarchy; • and c) further intercom~ects these symbols using a rich system of semmltic and discourse-pragmatic relations defined among the concepts" (Mahesh and Nirenburg 1995: 1). The function of the ontology is to supply "world knowledge to lexical, syntactic, and semantic processes" (ibid). The lexicon in MikroKosInos "mediates between the TMR ,and ontology" (Onyshkevyeh and Nirenburg 1994: 2). Lexicon entries for most open-class lexieal items represent word and plu:ase senses, which c~m be either directly mapped into ontological concepts or derived by locally (that is, in the lexicon entry itself) modifying constraints on property wducs of concepts used to specify the meaning of the given lexical item. L6xicalsenmntie information as well as clues for contextual semantic and pragmatic processing are typically located in the lexicon, adjectives being no exception. In the following section we illustrate file structnre of those parts of the lexicon entry in MikroKosmos which bear on the description of adjectival memfing. 2. The Ontological Approach to the Meaning of a Typical Adjective A simple, l~rototypical case of adjectival modification is a scalar adjective, which modifies a noun both syntactically and semantically. Our microtheory associates its meaning with a region on a scale which is defined as the range of ml ontological property (cf. Carlson and Nix~enburg, 1990). Tile contribution that the adjective makes to the construction of a semantic dependency structure