Generalising Feature Interactions in Email

We report on a property-based approach to feature interaction analysis for a client-server email system. The model is based upon Hall’s email model [12] presented at FIW’00 [3], but the implementation is at a lower level of abstraction, employing non-determinism and asynchronous communication; it is a challenge to avoid deadlock and race conditions. Our analysis differs in two ways: interaction analysis is fully automated, based on model-checking the entire state-space, and the results are scalable, that is they generalise to email systems consisting of any number of email clients. Abstraction techniques are used to prove the general results. The key idea is to model-check a system consisting of a constant number (m) of client processes, in parallel with a mailer process and an “abstract” process which represents the product of any number of other (possibly featured) client processes. We give a lower bound for the value of m. All of the models – for any specified set of client processes and selected features – are generated automatically using Perl scripts.