On the Expressive Power of Process Interruption and Compensation

The investigation of the foundational aspects of linguistic mechanisms for programming long running transactions (such as the scope operator of WS-BPEL) has recently renewed the interest in process algebraic operators that interrupt the execution of one process, replacing it with another one called the compensation. We investigate the expressive power of two of such operators, the interrupt operator of CSP and the try-catch operator for exception handling. We consider two non Turing powerful fragments of CCS (without restriction and relabeling, but with either replication or recursion). We show that the addition of such operators strictly increases the expressive power of the calculi. The calculi with replication and either interrupt or try-catch turn out to be weakly Turing powerful (Turing Machines can be encoded but only nondeterministically). The calculus with recursion is weakly Turing powerful when extended with interrupt, but it is Turing complete (Turing Machine can be modeled deterministically) when extended with try-catch.