A situated ontology is a world model used as a computational resource for solving a particular set of problems. It is treated as neither a "natural" entity waiting to be discovered nor a purely theoretical construct. This paper describes how a semantico-pragmatic analyzer, Mikrokosmos, uses knowledge from a situated ontology as well as from language-specific knowledge sources (lexicons and microtheory rules). Also presented are some guidelines for acquiring ontological concepts and an overview of the technology developed in the Mikrokosmos project for large-scale acquisition and maintenance of ontological databases. Tools for acquiring, maintaining, and browsing ontologies can be shared more readily than ontologies themselves. Ontological knowledge bases can be shared as computational resources if such tools provide translators between different representation formats. 1 A Situated Ontology World models (ontologies) in computational applications are artificially constructed entities. ...

This paper describes techniques for automatic construction of dictionaries for use in large-scale foreign language tutoring (FLT) and interlingual machine translation (MT) systems. The dictionaries are based on a language-independent representation called lexical conceptual structure (LCS). A primary goal of the LCS research is to demonstrate that synonymous verb senses share distributional patterns. In this paper, we show how the syntax-semantics relation can be used to develop a lexical acquisition approach that contributes both toward the enrichment of existing online resources and toward the development of lexicons containing more complete information than is provided in any of these resources alone. We start by describing the structure of the LCS and showing how this representation is used in FLT and MT. We then focus on the problem of building LCS dictionaries for large-scale FLT and MT. First, we describe authoring tools for manual and semi-automatic construction of LCS dictionaries; we then present a more sophisticated approach that uses linguistic techniques for building word defmitions automatically. These techniques have been implemented as part of a set of lexicon-development tools used in the MILT FLT project (Dorr et al., 1995; Sams, 1995; Weinberg et al., 1995) and in the PRINCITRAN MT project (Dorr et al., 1995b).

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. Our goal is to construct large-scale lexicons for interlingual MT of English, Arabic, Korean, and Spanish. We describe techniques that predict salient linguistic features of a nonEnglish word using the features of its English gloss (i.e., translation) in a bilingual dictionary. While not exact, owing to inexact glosses and language-to-language variations, these techniques can augmentan existing dictionary with reasonable accuracy, thus saving significant time. We have conducted two experiments that demonstrate the value of these techniques. The first tested the feasibility of building a database of thematic grids for over 6500 Arabic verbs based on a mapping between English glosses and the syntactic codes in Longman's Dictionary of Contemporary English (LDOCE) (Procter, 1978). We show that it is more efficient and less error-prone to hand-verify the automatically constructed grids than it would be to build the thematic grids by hand from scratch. The second experiment tested the auto...

lexicons from machine-readable resources. We describe semantic filters designed to reduce the number of incorrect assignments (i.e., improve precision) made by a purely syntactic technique. We demonstrate that it is possible to use these filters to build broad-coverage lexicons with minimal effort, at a depth of knowledge that lies at the syntax-semantics interface. We report on our results of disambiguating the verbs in the semantic filters by adding WordNet sense annotations. We then show the results of our classification on unknown words and we evaluate these results.

. This work belongs to a family of research efforts, called microtheories and aimed at describing the static meaning of all lexical categories in several languages in the framework of the MikroKosmos project on computational semantics. The latter also involves other static microtheories describing world knowledge and syntax-semantics mapping as well as dynamic microtheories connected with the actual process of text analysis. This paper describes our approach to determining and representing adjectival meaning, compares it with the body of knowledge on adjectives in literature and presents a detailed, practically tested methodology and heuristics for the acquisition of lexical entries for adjectives. The work was based on the set of over 6,000 English and about 1,500 Spanish adjectives obtained from task-oriented corpora. Introduction The topic of this paper is the information about adjectival meaning which should be included in a computational lexicon. Thus, we concentrate on...

The modern computational lexical semantics reached a point in its development when it has become necessary to define the premises and goals of each of its several trends. This paper proposes ten choices in terms of which these premises and goals can be discussed. It is argued that the central questions include the use of lexical rules for generating word senses; the role of syntax, pragmatics, and formal semantics in the specification of lexical meaning; the use of a world model, or ontology, as the organizing principle for lexical-semantic descriptions; the use of rules with limited scope; the relation between static and dynamic resources; the commitment to descriptive coverage; the trade-off between generalization and idiosyncracy; and, finally, the adherence to the "supply-side" (method-oriented) or "demand-side" (task-oriented) ideology of research. The discussion is inspired by, but not limited to, the comparison between the generative lexicon approach and the ontologi...

In the field of natural language processing (NLP) there is now a consensus that all NLP systems that seek to represent and manipulate meanings of texts need an ontology, that is a taxonomic classification of concepts in the world to be used as semantic primitives. In our continued efforts to build a multilingual knowledge-based machine translation (KBMT) system using an interlingual meaning representation, we have developed an ontology to facilitate natural language interpretation and generation. The central goal of the Mikrokosmos project is to develop a computer system that produces a comprehensive Text Meaning Representation (TMR) for an input text in any of a set of source languages. Knowledge that supports this process is stored both in language-specific knowledge sources (such as a lexicon) and in an independently motivated, language-neutral ontology of concepts in the world.

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. Treatment of meaning in NLP is greatly facilitated if semantic analysis and generation systems rely on a language-neutral, independently motivated world model, or ontology. However, the benefits of the ontology are somewhat offset in practice by the difficulty of its acquisition. This is why a number of computational linguists make a conscious choice to bypass ontology in their semantic deliberations. This decision is often justified by questioning the principles underlying ontologies and by challenging the ontology-based semantic enterprise on the grounds of its ostensible irreproducibility. In this paper we illustrate, on the example of the lexicon entry for the Spanish verb dejar, the expressive power of lexical-semantic descriptions based on the ontology used in the Mikrokosmos machine translation project. This expressive power is compared with that of some of the non-ontological approaches to lexical semantics. We argue that these approaches in reality rely on ontologies in ever...