Abstract
An uncertain database db is defined as a database in which distinct tuples of the same relation can agree on their primary key. A repair (or possible world) of db is then obtained by selecting a maximal number of tuples without ever selecting two distinct tuples of the same relation that agree on their primary key. Given a query Q on db, the certain answer is the intersection of the answers to Q on all repairs. Recently, a syntactic characterization was obtained of the class of acyclic self-join-free conjunctive queries for which certain answers are definable by a first-order formula, called certain first-order rewriting [15]. In this article, we investigate the nesting and alternation of quantifiers in certain first-order rewritings, and propose two syntactic simplification techniques. We then experimentally verify whether these syntactic simplifications result in lower execution times on real-life SQL databases.
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Decan, A., Pijcke, F., Wijsen, J. (2012). Certain Conjunctive Query Answering in SQL. In: Hüllermeier, E., Link, S., Fober, T., Seeger, B. (eds) Scalable Uncertainty Management. SUM 2012. Lecture Notes in Computer Science(), vol 7520. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-33362-0_12
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