Paper Info
Title
Certain Answers as Objects and Knowledge.
Abstract
The standard way of answering queries over incomplete databases is to compute certain answers, defined as the intersection of query answers on all complete databases that the incomplete database represents. But is this universally accepted definition correct? We argue that this one-size-fits-all definition can often lead to counterintuitive or just plain wrong results, and propose an alternative framework for defining certain answers. The idea of the framework is to move away from the standard, in the database literature, assumption that query results be given in the form of a database object, and to allow instead two alternative representations of answers: as objects defining all other answers, or as knowledge we can deduce with certainty about all such answers. We show that the latter is often easier to achieve than the former, that in general certain answers need not be defined as intersection, and may well contain missing information in them. We also show that with a proper choice of semantics, we can often reduce computing certain answers - as either objects or knowledge - to standard query evaluation. We describe the framework in the most general way, applicable to a variety of data models, and test it on three concrete relational semantics of incompleteness: open, closed, and weak closed world.
Year
DOI
Venue
2014
10.1016/j.artint.2015.11.004
Artificial Intelligence
Keywords
DocType
Volume
Incomplete information,Database queries,Certain answers,Data models,Certain knowledge,Open and closed world,Efficient computation
Conference
232
Issue
ISSN
Citations 
C
0004-3702
15
PageRank 
References 
Authors
0.63
34
1
Name
Order
Citations
PageRank
Leonid Libkin13446764.02