On global transaction scheduling criteria in multidatabase systems

A theoretical basis for global transaction scheduling to maintain global serializability in multidatabase systems is presented. Three correctness criteria are formulated to utilize the intrinsic characteristics of global transactions at the global level to determine the serialization order of global subtransactions at each local site. In particular, two new types of serializability, chain-conflicting serializability and sharing serializability, are proposed, and an optimal criterion (termed hybrid serializability) combining these two basic criteria is discussed. These criteria offer the advantage of imposing no restrictions on local sites while retaining global serializability. In addition, the optimal aspect of hybrid serializability defines limits on global serializability in multidatabase systems