Title 



Relative information completeness
 
Author 



 
Abstract 



This article investigates the question of whether a partially closed database has complete information to answer a query. In practice an enterprise often maintains master data Dm, a closedworld database. We say that a database D is partially closed if it satisfies a set V of containment constraints of the form q(D) ⊆ p(Dm), where q is a query in a language LC and p is a projection query. The part of D not constrained by (Dm, V) is open, from which some tuples may be missing. The database D is said to be complete for a query Q relative to (Dm, V) if for all partially closed extensions D′ of D, Q(D′) = Q(D), i.e., adding tuples to D either violates some constraints in V or does not change the answer to Q. We first show that the proposedmodel can also capture the consistency of data, in addition to its relative completeness. Indeed, integrity constraints studied for data consistency can be expressed as containment constraints. We then study two problems. One is to decide, given Dm, V, a query Q in a language LQ, and a partially closed database D, whether D is complete for Q relative to (Dm, V). The other is to determine, given Dm, V and Q, whether there exists a partially closed database that is complete for Q relative to (Dm, V).We establish matching lower and upper bounds on these problems for a variety of languages LQ and LC. We also provide characterizations for a database to be relatively complete, and for a query to allow a relatively complete database, when LQ and LC are conjunctive queries.   
Language 



English
 
Source (journal) 



ACM transactions on database systems.  New York, N.Y., 1976, currens  
Publication 



New York, N.Y. : 2010
 
ISSN 



03625915
15574644 [online]
 
Volume/pages 



35:4(2010), p. 127
 
Article Reference 



27
 
ISI 



000285294300005
 
Medium 



Eonly publicatie
 
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