Behavior Protocols Capturing Errors and Updates∗

We discuss the problem of defining a composition operator in behavior protocols in a way which would reflect false communication of the software components being composed. Here the issue is that the classical way in the ADLs supporting behavior description, such as Wright and TRACTA, is to employ a CSP-like parallel composition which inherently yields only ”successful traces”, ignoring nonaccepted attempts for communication. We show that, resulting from component composition, several types of behavior errors can occur: bad activity, no activity, and divergence. The key idea behind bad activity is that the asymmetry of roles during event exchange typical for real programs should be honored: the caller is considered to be the initiator of the call (callee has only a passive role). In most formal systems, this is not the case. We propose a new composition operator, ”consent”, reflecting these types of errors by producing erroneous traces. In addition, by using the consent operator, it can be statically determined, whether the atomicity of a dynamic update of a component is implicitly guarantied thanks to the behavior of its current environment.