Analyzing Conversations: Realizability, Synchronizability, and Verification

Conversations provide an intuitive and simple model for analyzing interactions among composite web services. A conversation is the global sequence of messages exchanged among the peers participating to a composite web service. Interactions in a composite web service can be analyzed by investigating the temporal properties of its conversations. Conversations can be specified in a top-down or bottom-up manner. In a top-down conversation specification, the set of conversations is specified first, without specifying the individual behaviors of the peers. In a bottom-up conversation specification, on the other hand, behavior of each peer is specified separately and the conversation set is defined implicitly as the set of conversations generated by these peers. For both top-down and bottom-up specification approaches we are interested in the following: 1) Automatically verifying properties of conversations, and 2) Investigating the effect of asynchronous communication on the conversation behavior. These two issues are closely related since asynchronous communication with unbounded queues increases the difficulty of automated verification significantly. In this paper, we give an overview of our earlier results on analysis and verification of conversations. We discuss two analysis techniques for identifying bottom-up and top-down conversation specifications that can be automatically verified. Synchronizability analysis identifies bottom-up conversation specifications for which the conversation set remains the same for asynchronous and synchronous communication. Realizability analysis, on the other hand, identifies top-down conversation specifications which can be implemented by a set of finite state peers interacting with asynchronous communication. We discuss sufficient conditions for synchronizability and realizability analyses which are implemented in our Web Service Analysis Tool (WSAT). WSAT can be used for verification of LTL properties of both top-down and bottom-up conversation specifications.