Theoretical foundations for compensations in flow composition languages

Abstract

A key aspect when aggregating business processes and web services is to assure transactional properties of process ex-ecutions. Since transactions in this context may require long periods of time to complete, traditional mechanisms for guaranteeing atomicity are not always appropriate. Gen-erally the concept of long running transactions relies on a weaker notion of atomicity based on compensations. For this reason, programming languages for service composition cannot leave out two key aspects: compensations, i.e. ad hoc activities that can undo the effects of a process that fails to complete, and transactional boundaries to delimit the scope of a transactional flow. This paper presents a hierarchy of transactional calculi with increasing expressiveness. We start from a very small language in which activities can only be composed sequentially. Then, we progressively introduce parallel composition, nesting, programmable compensations and exception handling. A running example illustrates the main features of each calculus in the hierarchy.