A. Makni, R. Bouaziz, and F. Gargouri (Tunisia)
Temporal databases, Concurrency control, Strong consistency, Optimistic method, Model checking, SPIN.
We propose in this paper a new optimistic access concurrency control algorithm for valid-time databases. An optimistic concurrency controller maintains for snapshot relations two sets for each transaction: a read set and a write set. In the case of valid-time relations, we continue to use one read set, but we define three different write sets rather than one. Indeed, we consider that insert, update and delete operations are three different writing types. With this proposal, the problem of false conflict detection is avoided. We also define a new type of granule, i.e. conflict object. In valid-time relation, this granule is not defined as a tuple, but as a temporal interval during which a tuple is valid. It allows reducing the risk of false conflict detection to the minimum. Moreover, our algorithm is able to retrieve and to correct problems concerning the operation failure risk. As for its validation, it is achieved first under a theoretical formalism, then under the SPIN model checker. Errors of blocking type are then avoided and safety properties, specified by temporal logic formulae, are guaranteed.
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