Model-Checking Web Services Business Activity Protocols

Web Services Business Activity specification defines two coordination protocols BAwCC (Business Agreement with Coordination Completion) and BAwPC (Business Agreement with Participant Completion)that ensure a consistent agreement on the outcome of long-running distributed applications. In order to verify fundamental properties of the protocols we provide formal analyses in the model checker UPPAAL.Our analyses are supported by a newly developed tool chain,where in the first step we translatetables with state-transition protocol descriptionsinto an intermediate XML format, and in the second step we translate this format into a network of communicating state machines directly suitable for verification in UPPAAL.Our results show that the WS-BA protocols, as described in the standard specification, violate correct operation by reaching invalid statesfor all underlying communication media except for a perfect FIFO. Hence we propose changes to the protocols and a further investigation of the modified protocols suggests that in case of the BAwCC protocol messages should be received in the same order as they are sent to preserve correct behaviour,while BAwPC is now correct even for asynchronous,unordered, lossy and duplicating media.Another important property of communication protocols is that all parties always reach, under certain fairness assumptions, their final states. Based on an automatic verification with different communication models, we prove that our enhanced protocols satisfy this property whereas the original protocols do not.All verification results presented in this article were performedin a fully automatic way using our new tool csv2uppaal