Minimal recursion semantics (MRS) is a framework for computational semantics that is suitable for parsing and generation and that can be implemented in typed feature structure formalisms. We discuss why, in general, a semantic representation with minimal structure is desirable and illustrate how a descriptively adequate representation with a nonrecursive structure may be achieved. MRS enables a simple formulation of the grammatical constraints on lexical and phrasal semantics, including the principles of semantic composition. We have integrated MRS with a broad-coverage HPSG grammar.

In this paper we present a formalization of the centering approach to modeling attentional structure in discourse and use it as the basis for an algorithm to track discourse context and bind pronouns. As described in [GJW86], the process of centering attention on entities in the discourse gives rise to the intersentential transitional states of continuing, re~aining and shifting. We propose an extension to these states which handles some additional cases of multiple ambiguous pronouns. The algorithm has been implemented in an HPSG natural language system which serves as the interface to a database query application.

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The lexicon now plays a central role in our implementation of a Head-driven Phrase Structure Grammar (HPSG), given the massive relocation into the lexicon of linguistic information that was carried by the phrase structure rules in the old GPSG system. HPSG's grammax contains fewer tha4z twenty (very general) rules; its predecessor required over 350 to achieve roughly the same coverage. This simplification of the grammax is made possible by an enrichment of the structure and content of lexical entries, using both inhcrit~nce mechanisms and lexical rules to represent thc linguistic information in a general and efficient form. We will argue that our mechanisms for structure-sharing not only provide the ability to express important linguistic generalizations about the lexicon, but also make possible an efficient, readily modifiable implementation that we find quite adequate for continuing development of a large natural language system.

This paper presents an analysis of quantifier and wh-operator scope in terms of a lexicalized theory of quantifier storage, within the framework of Head-Driven Phrase Structure Grammar. The proposed analysis provides an alternative to the derivational approach wherein quantifier scope is determined at a separate level of representation via movement, and shows how scope of quantifiers and wh-phrases (fronted or in situ) can be handled in a unified way in a constraint-based grammar. Lexicalization of quantifier storage offers an account of scope facts in raising and unbounded dependency constructions which have been problematic in an earlier constraint-based approach to quantifier scope.