Faster query answering in probalistic databases using read-once functions

A boolean expression is in read-once form if each of its variables appears exactly once. When the variables denote independent events in a probability space, the probability of the event denoted by the whole expression in read-once form can be computed in polynomial time (whereas the general problem for arbitrary expressions is #P-complete). Known approaches to checking read-once property seem to require putting these expressions in disjunctive normal form. In this paper, we tell a better story for a large subclass of boolean event expressions: those that are generated by conjunctive queries without self-joins and on tuple-independent probabilistic databases. We first show that given a tuple-independent representation and the provenance graph of an SPJ query plan without self-joins, we can, without using the DNF of a result event expression, efficiently compute its co-occurrence graph. From this, the read-once form can already, if it exists, be computed efficiently using existing techniques. Our second and key contribution is a complete, efficient, and simple to implement algorithm for computing the read-once forms (whenever they exist) directly, using a new concept, that of co-table graph, which can be significantly smaller than the cooccurrence graph. Disciplines Computer Sciences Comments Sudeepa Roy, Vittorio Perduca, and Val Tannen. 2011. Faster query answering in probabilistic databases using read-once functions. In Proceedings of the 14th International Conference on Database Theory (ICDT '11). ACM, New York, NY, USA, 232-243 doi: 10.1145/1938551.1938582 © ACM, 2011. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in Proceedings of the 14th International Conference on Database Theory , { (2011)} http://doi.acm.org/10.1145/1938551.1938582" Email [email protected] This conference paper is available at ScholarlyCommons: http://repository.upenn.edu/cis_papers/647 On the Limitations of Provenance for Queries With Difference ∗