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Abstract : |
Abstract. Consistency enforcement may be regarded as a process of transaction transformation, where the modied transaction will be consistent with respect to a given set of constraints. The computational approach by Schewe and Thalheim requires the modied transaction to be the greatest consistent one below the original transaction with respect to some order. The order should express the preservation of the \eect " of the original transaction. Thus, the major problem is to nd the right order. The rst choice, specialization, turns out to provide good computational properties, but on the one hand the order is too weak, because arbitrary changes to state variables not touched by the original transaction are allowed, and on the other hand it is too strong, as eect preservation by specialization means that further changes to the other state variables are forbidden. In this paper, modications of greatest consistent specializations are studied to avoid these problems. Weakening the notion of eect preservation leads to the denition of maximal consistent eect preservers (MCEs). This turns out to be a reasonable choice, since they preserve the computational strength achieved for consistent specializations. Moreover, for basic operations they are compatible with dierent consistency enforcement strategies chosen by users. 1, |
