Experience of using a lightweight formal specification method for a commercial embedded system product line

A simple specification method is introduced and the results of its application to a series of projects in Philips are reported. The method is principally designed to ensure that that every unusual scenario is considered in a systematic way. In practice, this has led to highquality specifications and accelerated product development. While the straightforward tabular notation used has proved readily understandable to non-technical personnel, it is also a formal method, producing a model of system behaviour as a finite state machine. In this respect, the notation is unusual in being designed to preserve as far as possible a view of the overall system state and how this changes. The notation also features a constraint table which may be described as a kind of spreadsheet for invariants to help define the states of the system.