S. All local authors can be reached via e-mail at the address last-name@cs.unibo.it. Questions and comments should be addressed to tr-admin@cs.unibo.it. Recent Titles from the UBLCS Technical Report Series 97-4 An Algebra of Actors, M. Gaspari, G. Zavattaro, May 1997. 97-5 On the Turing Equivalence of Linda Coordination Primitives, N. Busi, R. Gorrieri, G. Zavattaro, May 1997 (Revised October 1998). 97-6 A Process Algebraic View of Linda Coordination Primitives, N. Busi, R. Gorrieri, G. Zavattaro, May 1997. 97-7 Validating a Software Architecture with respect to an Architectural Style, P. Ciancarini, W. Penzo, July 1997. 97-8 System Support for Partition-Aware Network Applications, O. Babaoglu, R. Davoli, A. Montresor, R. Segala, October 1997. 97-9 Generalized Semi-Markovian Process Algebra, M. Bravetti, M. Bernardo, R. Gorrieri, October 1997. 98-1 Group Communication in Partitionable Systems: Specification and Algorithms, O. Babao glu, R. Davoli, A. Montresor, April 1998. 98-2...

The semantic definition of action refinement on labelled configuration structures is compared with the notion of syntactic substitution, which can be used as another notion of action refinement in a process algebraic setting. The comparison is done by studying a process algebra equipped with sequential composition, parallel composition with an explicit synchronisation set, and an operator for action refinement. On the one hand, the language (including the refinement operator) is given a configuration structure semantics. On the other hand, a reduction procedure transforms a process term P into a flat term (i.e., with the refinement operator not occurring in it) red(P) by means of syntactic substitution, defined in a structural inductive way. The main aim of the paper is to investigate general conditions under which the terms P and red(P) have the same semantics. The results we present are essentially dependent on the question whether the refined action can be synchronised or not. In the latter case, P and red(P) give rise to isomorphic configuration structures under mild assumptions. The former case is considerably more difficult, since then refinement cannot be expected to distribute over parallel composition. We give necessary and sufficient semantic conditions under which distribution still holds up to semantic equivalence. Subsequently, we also give sufficient (but not necessary) syntactic conditions for reducible terms. Finally, we generalise these results to a language with recursion.] 1996 Academic Press, Inc. 1.

this paper different properties of systems which are invariant under refinement are investigated: relationsships between systems (e.g. equivalences) and general properties of systems as e.g. deadlock-freeness.

We consider a process calculus that combines reactivity and atomicity. Reactivity means that process behaviors are made of reactions that are sequences of rewritings. Atomicity means that there exists an operator to deal with non terminating reactions. Processes can make or forbid actions. Reaction does not terminate when a process tries to make a forbidden action, or conversely, to forbid an already made action. R'esum'e On consid'ere un calcul de processus qui combine r'eactivit'e et atomicit'e. R'eactivit'e signifie que les comportements des processus sont des s'equences de r'eactions, chaque r'eaction 'etant elle-meme une suite de r'e'ecritures. Atomicit'e signifie qu'il existe un op'erateur pour traiter les r'eactions qui ne terminent pas. Lors de leur r'eactions, les processus peuvent effectuer ou interdire des actions. Une r'eaction d'un processus ne termine pas lorsque celui-ci tente d'effectuer et d'interdire une meme action durant cette r'eaction. 1 Introduction The notio...

In the design process of distributed systems we may have to replace abstract specifications of components by more concrete specifications, thus providing more detailed design information. In the context of process algebra, this well-known approach is often referred to as action refinement. We study the relationships between action refinement and security properties within the Security Process Algebra (SPA). First we formalize the concept of action refinement as a structural inductive transformation. Then we prove several compositional results which can be exploited in the stepwise development of processes. Finally, we consider information flow security properties for SPA processes and define a decidable class of secure processes which is closed under refinement.