Component composition errors and update atomicity: static analysis

摘要

Dynamic evolution inherently involves dynamic update and the issue of its atomicity. We show how this issue can be addressed in a similar manner to a communication failure via an extension to behavior protocols. First, we discuss the problem of defining a composition operator for behavior protocols so as to be able to reflect communication failures. Classical architecture description languages (ADLs) supporting behavior description, such as Wright and TRACTA, use a CSP-like parallel composition, which inherently yields only 'successful traces' ignoring non-accepted communication attempts. We show that component composition can produce several different types of behavior errors: bad activity, no activity, and divergence. The key idea behind bad activity is that real programs typically have an asymmetry of roles during event exchange: the caller is considered to be the initiator of the call while the callee has only a passive role. This contrasts with most formal systems, which treat communication symmetrically. We propose a new composition operator, 'consent', which reflects these types of errors by producing erroneous traces. By using the consent operator it can be statically determined whether the atomicity of a dynamic update of a component is implicitly guaranteed by the behavior of its current environment.