Open and Closed World Assumptions in Data Exchange
نویسندگان
چکیده
Data exchange is the problem of finding an instance of a target schema, given an instance of a source schema and a specification of a mapping between the source and the target schemas, and answering queries over target instances. A schema mapping is a condition, often expressed in a fragment of first-order logic, that relates instances of source and target schemas. Most commonly it is a conjunction of sentences of the form
منابع مشابه
On Closed World Data Bases / 119 on Closed World Data Bases
Deductive question-answering systems generally evaluate queries under one of two possible assumptions which we in this paper refer to as the open and closed world assumptions. The open world assumption corresponds to the usual first order approach to query evaluation: Given a data base DB and a query Q, the only answers to Q are those which obtain from proofs of Q given DB as hypotheses. Under ...
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