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Author Reiter, Raymond
Source ACM Digital Library
Content type Text
Publisher Association for Computing Machinery (ACM)
File Format PDF
Copyright Year ©1980
Language English
Subject Domain (in DDC) Computer science, information & general works ♦ Data processing & computer science
Abstract A class of first-order databases with no function signs is considered. A closed database DB is one for which the only existing individuals are those explicitly referred to in the formulas of DB. Formally, this is expressed by including in DB a domain closure axiom $(\textit{x})\textit{x}$ = $\textit{c}1$ ∨···∨ $\textit{x}$ = $\textit{cp},$ where $\textit{c}1,…,\textit{cp}$ are all of the constants occurring in DB. It is shown how to completely capture the effects of this axiom by means of suitable generalizations of the projection and division operators of relational algebra, thereby permitting the underlying theorem prover used for query evaluation to ignore this axiom.A database is E-saturated if all of its constants denote distinct individuals. It is shown that such databases circumvent the usual problems associated with equality, which arise in more general databases.Finally, it is proved for Horn databases and positive queries that only definite answers are obtained, and for databases with infinitely many constants that infinitely long indefinite answers can arise.
ISSN 00045411
Age Range 18 to 22 years ♦ above 22 year
Educational Use Research
Education Level UG and PG
Learning Resource Type Article
Publisher Date 1980-04-01
Publisher Place New York
e-ISSN 1557735X
Journal Journal of the ACM (JACM)
Volume Number 27
Issue Number 2
Page Count 15
Starting Page 235
Ending Page 249


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Source: ACM Digital Library