On Herbrand Semantics and Conflict Serializability of Read-Write Transactions (Extended Abstract)

The quest for unified correctness criteria in database concurrency control is addressed from a new perspective. A family of Herbrand semantics is presented, where each semantics provides an interpretation for operations in the read-write model of transactions. Using commutativity arguments, each semantics leads to a notion of conflict, which then gives rise to distinct classes of serializable schedules. Surprisingly, the classical notion of serializability with respect to two of these semantics, update-in-place and deferred-update semantics, already embodies a unified correctness criterion; moreover, prefix-closed variants of it allow for a higher degree of transaction parallelism than, for example, prefix-reducibility. Finally, it is shown that previous criteria may permit undesirable schedules, which are ruled out by a stronger notion of serializability that captures all intuitively correct schedules, but is incomparable to prefix-reducibility and the classes of schedules recognized by optimistic protocols.