Automating Compensation in a Multidatabase t

Compensation is the process b y which a committed transaction in a database is undone b y running the semantic inverse o f that transaction on the database. Compensation has been proposed as a technique for undoing committed work in various situations where strict atomicity cannot be maintained [GS87, MR91]. In this paper, we discuss compensation i n longrunning multidatabase transactions. W e define the step approach to integrating local database schemas into a mulitdatabase. In the step approach, each local database is encapsulated b y a set of procedures (steps). Steps can be grouped into atomic global transactions. Each step also has an associated compensating step, which is called i f the compensating transaction is run. We examine two areas of multidatabase transaction management where compensation is required. The first is implementing compensation as a recovery technique when an open nested transaction is aborted. The second is in backing out the eflects of an atomic multidatabase transaction when some local database transaction commits before a global abort decision is made.