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 to resolve because the the behavior or even the existence of local transactions is not known to the multidatabase system. To overcome these problems, we propose to incorporate additional data manipulationoperations in the subtransactions of each multidatabase transaction. We show that if these operations create direct conflicts between subtransactions 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 an...

To enforce global serializability in a multidatabase environment themultidatabase transaction manager must take into account the indirect (transitive) conflicts between multidatabase transactions caused by local transactions. Such conflicts are difficult to resolve because the behavior or even the existence of local transactions is not known to the multidatabase system. To overcome these difficulties, 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 subtransactions 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 optimistic and conservative multidatabase 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 by preventing multidatabase transactions from being serialized in different ways at the participating database systems. Refinements of these methods are also proposed for multidatabase environments where the participating database systems allow schedules that are cascadeless or transactions have analogous execution and serialization orders. In particular, we show that forced local conflicts can be eliminated in rigorous local systems, local cascadelessness simplifies the design of a global scheduler and that local strictness offers no significant advantages over cascadelessness.

A Transaction Specification and Management Environment (TSME) is a programmable system that supports: (i) implementation-independent specification of application-specific extended transaction models (ETMs), and (ii) configuration of transaction management mechanisms (TMMs) to enforce specified ETMs. The TSME can ensure correctness and reliability while allowing the functionality required by workflows and other advanced applications that require access to multiple heterogeneous, autonomous, and/or distributed (HAD) systems. To support ETM specification, the TSME provides a transaction specification language that describes dependencies between transactions. Unlike other transaction specification languages, TSME's dependency descriptors use a common set of primitives, and are enforceable, i.e., can be evaluated at any time during transaction execution to determine whether operations issued violate ETM specifications. To determine whether an ETM can be enforced in a specific HAD system env...

A variety of extensions to the traditional (ACID) transaction model have resulted in a plethora of extended transaction models (ETMs). Many of these ETMs are application-specific, i.e., they are designed to provide correctness guarantees adequate for a particular application, but not others. Similarly, an application-specific ETM may impose restrictions that are unacceptable in one application, yet required in another. To define new ETMs, to determine whether an ETM is appropriate for an application, and to integrate ETMs to produce new ETMs, we need a framework for ETM specification and reasoning. In this paper, we describe such a framework. Our framework supports implementation-independent specification of ETMs described in terms of dependencies between transactions. Dependencies are specified using dependency descriptors. Unlike other transaction specification frameworks, dependency descriptors use a common set of primitives, and are enforceable, i.e., can be evaluated at...

. Database applications often impose temporal dependencies between transactions that must be satisfied to preserve data consistency. The extant correctness criteria used to schedule the execution of concurrent transactions are either time independent or use strict, difficult to satisfy real-time constraints. On one end of the spectrum, serializability completely ignores time. On the other end, deadline scheduling approaches consider the outcome of each transaction execution correct only if the transaction meets its real-time deadline. In this paper, we explore new correctness criteria and scheduling methods that capture temporal transaction dependencies and belong to the broad area between these two extreme approaches. We introduce the concepts of succession dependency and chronological dependency and define correctness criteria under which temporal dependencies between transactions are preserved even if the dependent transactions execute concurrently. We also propose a chronological s...