Multidatabase transaction management scheme supporting multiple subtransactions of a global transaction at a site

The purpose of multidatabase systems is to allow users to access and manipulate data from existing databases in the distributed environment without modifying the existing database management systems (DBMSs). In the multidatabase environment, determining if a schedule for a set of global transactions is globally serializable is difficult because each local DBMS operates autonomously. Thus, we adopt the approach that relaxes the isolation and atomicity requirements of transactions. Moreover, in some applications, multiple subtransactions of a global transaction need to be submitted to a local site. To support this new transaction model, we propose a new correctness criterion for global schedules that is based on the semantic compatibility of global transactions. The conditions that global transactions should satisfy to ensure the correct executions are investigated, and the concept of well-formed global transaction is defined. We also present a concurrency control scheme that ensures the proposed correctness criterion. Our scheme uses both compensation and retrial techniques to eliminate the requirement of local prepare-to-commit operations, and hence it allows the global subtransactions to be committed unilaterally at local. sites before the decision of global commit. (C) Elsevier Science Inc. 1997