Expressive flexibility in constraint-oriented specification: LOTOS and Co-notation

We illustrate and compare the flexibility of two specifìcation techniques for concurrent systems, namely LOTOS and our recent constraint-oriented specification notation ('Co-notation'). Flexibility is intended here as the ability to match as closely as possible the structure of the initial. informal behavioural description of the System, and to directly formalize the conceptual links among data variables and events, and their groupings, as identified by that description. We show that the simple yet powerful composition operator of the co-notation (constraint conjunction), supporting both shared-action (rendez-vous) and shared variable process interactions. achieves a higher expressive flexibility than LOTOS, and a stronger support of constraint-oriented reasoning.