Probabilistic Object Bases Probabilistic Object Bases Revised Version, April 2001

Though there are many applications where an object oriented data model is a good way of representing and querying data, current object database sy t ms are unable to handle objects whose attributes are uncertain. In this paper, we extend pre vious pioneering work by Kornatzky and Shimony to develop an algebra to handle object bases with unc ertainty. We propose concepts of consistency for such object bases, together with an NP-complet eness result, and classes of probabilistic object bases for which consistency is polynomially checkab le. In addition, as certain operations involve conjunctions and disjunctions of events, and as the probability of conjunctive and disjunctive events depends both on the probabilities of the primiti ve events involved as well as on what is known (if anything) about the relationship between the ev nts, we show how all our algebraic operations may be performed under arbitrary probabilistic conjunction and disjunction strategies. We also develop a host of equivalence results in our algebra, which may be used as rewrite rules for query optimization. Last but not least, we have develope d a prototype probabilistic object base server on top of ObjectStore. We describe experiments to ass ess the efficiency of different possible rewrite rules. 1Institut und Ludwig Wittgenstein Labor für Informationss ysteme, Technische Universität Wien, Favoritenstraße 9–11, A-1040 Wien, Austria. E-mail: feiter, lukasiewicz g@kr.tuwien.ac.at 2Department of Computer Science, Bucknell University, Lewi sburg, PA 17837, USA. E-mail: jameslu@bucknell.edu 3Institute for Advanced Computer Studies, Institute for Sys tems Research and Department of Computer Science, University of Maryland, College Park, Maryland 20742, USA. E-mail: vs@cs.umd.edu Acknowledgements: This work were supported by a TASC/DARPA grant J09301S9806 1, by the Army Research Laboratory under contract number DAAL01-97-K013 5, by an NSF Young Investigator award IRI93-57756 and an NSF grant CCR9731893, and by the Austrian Sci ence Fund under project N Z29-INF. Copyright c 2001 by the authors INFSYS RR 1843-99-11 I

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