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Relating Communicating Processes with Different Interfaces

Burton J., Koutny M., Pappalardo G.

Fundamenta Informaticae

2004

Vol. 59, nr 1

1-37

We present here an implementation relation intended to formalise the notion that a system built of communicating processes is an acceptable implementation of another base, or target, system in the event that the two systems have different interfaces. Such a treatment has clear applicability in the software development process, where (the interface of) an implementation component may be expressed at a different level of abstraction to (the interface of) the relevant specification component. Technically, processes are formalised using Hoare's CSP language, with its standard failures-divergences model. The implementation relation is formulated in terms of failures and divergences of the implementation and target processes. Interface difference is modelled by endowing the implementation relation with parameters called extraction patterns. These are intended to interpret implementation behaviour as target behaviour, and suitably constrain the former in connection to well-formedness and deadlock properties. We extend the results of our previous work and replace implementation relations previously presented by a single, improved scheme. We also remove all the restrictions previously placed upon target processes. Two basic kinds of results are obtained: realisability and compositionality. The latter means that a target composed of several connected systems may be implemented by connecting their respective implementations. The former means that, if target and implementation in fact have the same interface, then the implementation relation they should satisfy collapses into standard implementation pre-order. We also show how to represent processes and extraction patterns in a manner amenable to computer implementation, and detail a graph-theoretic restatement of the conditions defining the implementation relation, from which algorithms for their automatic verification are easily derived.

Behaviour Abstraction for Communicating Sequential Processes

Koutny M., Pappalardo G.

Fundamenta Informaticae

2001

Vol. 48, nr 1

21-54

We investigate the notion that a system is an acceptable implementation of another base or target system, in the case that the two systems (or processes) have different interfaces. For instance, the base processes can be thought of as specifications, or ideal processes operating in an error-free environment, while the implementations model their actual realisations, operating in an error-prone environment and possibly employing a variety of fault-tolerant techniques. Using the CSP model, we relate implementations and base systems in terms of their observable behaviours. We obtain two fundamental results, viz. realisability and compositionality. The former ensures that implementations may be put to good use, while the latter guarantees that a target composed of several connected subsystems may be implemented by connecting their respective implementations.