Sequence-based global predicates for distributed computations : definitions and detection algorithms

We consider the problem of detecting sequences of predicates defined over global states of distributed computation. We introduce two new global predicate classes called simple sequences and interval-constrained sequences that define causally-ordered sets of desirable states along with intervening forbidden states. Our formalism is more general than former proposals and permits concise and intuitive expression of many interesting system properties. Algorithms are given for verifying formulas belonging to these predicate classes in an on-line and observer-independent manner during distributed computations. We illustrate the utility of our results by applying them to examples drawn from programs testing, debugging and dynamic reconfiguration in distributed systems