A computer system for inference execution and data retrieval
Communications of the ACM
Specifying queries as relational expressions: the SQUARE data sublanguage
Communications of the ACM
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Questions which involve 'all', 'every', 'some', or the indefinite article, pose some peculiar problems when presented to a computerized question-answering system where ambiguities cannot be tolerated. These problems vary from the nature of the correct answer in special cases to the very admissibility of the question itself. To deal with these problems it is convenient to divide questions into two classes---extensional questions whose answers are to name things or truth values, intensional questions whose answers are to give meanings. This paper examines extensional questions. For these, the interpretative problems arising with 'all' and 'every' can be solved by introducing a new kind of quantification, extensional universal quantification, that has the meaning of 'all F' together with a secondary meaning that the class F is not empty. Formal rules for this quantification are given, and it is shown that the so-called definite formulas (which explicate permissible queries) are closed under the new operator.