Workflows are composite activities that can be used to support and automate multisystem applications involving humans, heterogeneous databases and legacy systems. The traditional atomic transaction model, successful for centralized and homogeneous applications, is not suitable for supporting such workflows. Intertask dependencies, which are conditions involving events and dependencies among workflow tasks, are used to specify the coordination requirements among the workflow tasks and are a central component of most workflow models. They form a basis for developing a uniform formal framework for workflows, which is a key contribution of this work. In this paper, we formalize intertask dependencies using temporal logic. This involves event attributes, which are needed to determine whether a dependency is enforceable and to properly schedule events. Each dependency is represented internally as a finite state automaton that captures the computations that satisfy the given dependency. Sets of automata are combined into a scheduler that produces global computations satisfying all relevant dependencies, thus enacting the given workflow. This algorithm is rigorously proved correct; it has been implemented.
global serializability i n a m ultidatabase environment t h e m ultidatabase transaction manager must take i n to account the indirect (transitive) conicts between multidatabase transactions caused by l o c a l transactions. Such con icts are di cult to resolve because the behavior or even the existence of local transactions is not known to the multidatabase system. To o vercome these di culties, we propose to incorporate additional data manipulation operations in the subtransactions of each m ultidatabase transaction. We show that if these operations create direct con icts between subtransactions at each participating local database system, indirect con icts can be resolved even if the multidatabase system is not aware of their existence. Based on this approach, we i n troduce optimistic and conservative m ultidatabase transaction management methods that require the local database systems to assure only local serializability. The proposed methods do not violate the autonomy of the local database systems and guarantee global serializability b y p r e v enting multidatabase transactions from being serialized in di erent w ays at the participating database systems. Re nements of these methods are also proposed for multidatabase environments where the participating database systems allow s c hedules that are cascadeless or transactions have analogous execution and serialization orders. In particular, we s h o w that forced local con icts can be eliminated in rigorous local systems, local cascadelessness simpli es the design of a global scheduler and that local strictness o ers no signi cant a d v antages over cascadelessness. Keywords| m ultidatabase transactions, serializability, i ndirect con icts, tickets, analogous execution and serialization orders, rigorous scheduling
The main difficulty in enforcing global serializability in a multidatabase environment lies in resolving indirect (transitive) conflicts between multidatabase transactions. Indirect conflicts introduced by local transactions are difficult t o resolve because the the behavior or even the existence of local transactions is not known t o the multidatabase system. To overcome these problems, we propose to incorporate additional data manipulation operations in the subtransactions of each multidatabase transaction. We show that if these operations create direct conflicts between subtranaactions at each participating local database system, indirect conflicts can be resolved even if the multidatabase system is not aware of their existence. Based on this approach we introduce a multidatabase transaction management method that requires the local database systems to ensure only local serializability. The proposed method and its refinements do not violate the autonomy of the local database systems and guarantee global serializability by preventing multidatabase transactions from being serialized in different ways a t the participating database systems.
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