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Reasoning with Semantic-Enabled Qualitative Preferences
No full textPersonalized access to information is an important task in all real-world applications where the user is interested in documents, items, objects or data that match her preferences. Among qualitative approaches to preference representation, CP-nets play a prominent role: with their clear graphical structure, they unify an easy representation of user desires with nice computational properties when computing the best outcome. In this paper, we explore how to reason with CP-nets in the context of the Semantic Web, where preferences are linked to formal ontologies. We show how to compute Pareto optimal outcomes for a semantic-enabled CP-net by solving a constraint satisfaction problem, and we present complexity results related to different ontological language
Corrigendum to 'Counting Database Repairs that Satisfy Conjunctive Queries with Self-Joins'
Full text linkA remark on the complexity of consistent conjunctive query answering under primary key violations
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The conjunctive information in disjunctive databases
No full textpeer reviewedOR-sets and marked null values are two ways of representing incomplete information in relational databases. Existing relational database systems do not support OR-sets, but can be easily extended to support marked null values. We show that relations with OR-sets can be transformed into relations with marked null values without hanging the answers to conjunctive queries
On the consistent rewriting of conjunctive queries under primary key constraints
Full text linkpeer reviewedThis article deals with the computation of consistent answers to queries on relational databases that violate primary key constraints. A repair of such inconsistent database is obtained by selecting a maximal number of tuples from each relation without ever selecting two distinct tuples that agree on the primary key. We are interested in the following problem: Given a Boolean conjunctive query q, compute a Boolean first-order (FO) query @j such that for every database db, @j evaluates to true on db if and only if q evaluates to true on every repair of db. Such @j is called a consistent FO rewriting of q. We use novel techniques to characterize classes of queries that have a consistent FO rewriting. In this way, we are able to extend previously known classes and discover new ones. Finally, we use an Ehrenfeucht-Fraisse game to show the non-existence of a consistent FO rewriting for @?x@?y(R(x@?,y)@?R(y@?,c)), where c is a constant and the first coordinate of R is the primary key
On the first-order expressibility of computing certain answers to conjunctive queries over uncertain databases
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