# The ICICS/CS Reading Room

## UBC CS TR-77-16 Summary

- No on-line copy of this technical report is available.

- On Closed World Data Bases, October 1977 R. Reiter
Deductive question-answering system generally evaluate queries under one of
two possible assumptions which we in this paper refer to as the open and closed
world assumptions. The open world assumption corresponds to the usual first
order approach to query evaluation: Given a data base DB and a query Q, the only
answers to Q are those which obtain from proofs of Q given DB as hypotheses.
Under the closed world assumption, certain answers are admitted as a result
of failure to find a proof. More specifically, if no proof of a positive ground
literal exists, then the negation of that literal is assumed true.

In this paper, we show that closed world evaluation of an arbitrary query may be
reduced to open world evaluation of so-called atomic queries. We then show that
the closed world assumption can lead to inconsistencies, but for Horn data bases
no such inconsistencies can arise.

Presented at the Workshop on Logic and Data Bases, Toulouse, France,
November 16-18, 1977.

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