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Answers as Type ConstraintsAbstract:
This paper concerns systems that deal with information about classes of individuals rather than information about particular individuals. Accordingly, queries to such systems imply answers also given in terms of classes of individuals. To this end the notion of taxonomy as a hierarchical type system is introduced, together with a language for querying taxonomical systems. A query expressed in this language is either a declarative or an interrogative sentence. Declarative sentences correspond to the usual first-order formulae and require a “yes” or “no” answer. Interrogative sentences are basically declarative sentences with some variables stipulated as “query” variables, for which the required answers are type assignments to the query variables making the sentences true. It is shown that answers to queries are characterized denotationally in terms of types, which are operationally expressed as type constraints on specified variables to the queries. This is the kernel of a constraint logic programming system implementing the query language described in this paper.