Abstract
This paper focuses on the problem of answering queries addressed to a group of databases which share a common set of rules (deductive rules or integrity constraints). We assume that the databases are sets of clauses consistent with the rules. However, accessing them altogether may lead to contradictions.
We allow the user who queries the group of databases to specify, in his/her queries, an order between the databases he/she wants to access. This order is supposed to express the relative reliability between the databases. In the context of our work, we can guarantee that the answers the user will get, will not be contradictory.
The paper describes the axiomatics of a logic for reasoning with information provided by several databases which can be contradictory. It also presents a query-evaluator based on this logic. This evaluator is described as a meta-interpreter of PROLOG. We prove that, under some non-recursivity condition, this evaluator provides correct answers, in regard to the ones characterized by the logic.
This evaluator is flexible in the sense that it allows the user to ask hypothetical queries of the form: assuming that the relative reliability of some databases is given by such an order, is such a condition true? and also, hypothetical queries of the form: assuming that the relative reliability of some databases is given by such an order, what are the individuals which satisfy such a condition?
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Cholvy, L. (1997). Flexible Query-Answering in a Group of Databases. In: Andreasen, T., Christiansen, H., Larsen, H.L. (eds) Flexible Query Answering Systems. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-6075-3_8
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DOI: https://doi.org/10.1007/978-1-4615-6075-3_8
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