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Title
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Capturing missing tuples and missing values
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Author
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Abstract
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| Databases in real life are often neither entirely closed-world nor entirely open-world. Databases in an enterprise are typically partially closed, in which a part of the data is constrained by master data that contains complete information about the enterprise in certain aspects. It has been shown that, despite missing tuples, such a database may turn out to have complete information for answering a query. This article studies partially closed databases from which both tuples and attribute values may be missing. We specify such a database in terms of conditional tables constrained by master data, referred to as c-instances. We first propose three models to characterize whether a c-instance T is complete for a query Q relative to master data. That is, depending on how missing values in T are instantiated, the answer to Q in T remains unchanged when new tuples are added. We then investigate three problems, to determine (a) whether a given c-instance is complete for a query Q, (b) whether there exists a c-instance that is complete for Q relative to master data available, and (c) whether a c-instance is a minimal-size database that is complete for Q. We establish matching lower and upper bounds on these problems for queries expressed in a variety of languages in each of the three models for specifying relative completeness. |
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Language
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English
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Source (journal)
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ACM transactions on database systems. - New York, N.Y., 1976, currens
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Publication
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New York, N.Y.
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2016
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ISSN
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0362-5915
1557-4644
[online]
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DOI
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10.1145/2901737
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Volume/pages
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41
:2
(2016)
, 47 p.
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Article Reference
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10
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ISI
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000380095300004
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Medium
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E-only publicatie
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Full text (Publisher's DOI)
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Full text (publisher's version - intranet only)
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