Artificial Intelligence Events
Tuesday, November 24, 2009
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MS.05
Approximability and Parameterized Complexity of Minmax Values
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The Closed World Assumption: a technical presentation by Chris DateCS1.04The Closed World Assumption
a technical presentation by C. J. Date ABSTRACT The Closed World Assumption (CWA) is an extremely important concept in the database world, despite the fact that it isn't usually spelled out explicitly. Basically what it says is this: Everything stated by the database, either explicitly or implicitly, is true; everything else is false. This presentation explains the CWA in detail and shows why it's preferred over its rival, the Open World Assumption (OWA). In particular, it examines the claims that are sometimes heard to the effect that the database community operates under the CWA while the semantic web community operates under the OWA. It also explains how "missing information" can be handled without any need for nulls or three-valued logic. Topics Background review: what a database really is (?) Relation values vs. relation variables Relvar predicates and constraints The CWA and OWA defined Why the CWA is preferred Relvar predicates revisited Unknown and uncertain information Negation and disjunction |