This paper combines and extends the material of [GG-a/c/d/e], except for the part in [GG-c] on refinement of transitions in Petri nets and the discussion of TCSP-like parallel composition in [GG-e]. An informal presentation of some basic ingredients of this paper appeared as [GG-b]. Among others, the treatment of action refinement in stable and non-stable event structures is new. The research reported here was supported by Esprit project 432 (METEOR), Esprit Basic Research Action 3148 (DEMON), Sonderforschungsbereich 342 of the TU Munchen, ONR grant N00014-92-J-1974 and the Human Capital and Mobility Cooperation Network EXPRESS (Expressiveness of Languages for Concurrency). Contents

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s are available from the same host in the directory /pub/TR/UBLCS/ABSTRACTS in plain text format. All local authors can be reached via e-mail at the address last-name@cs.unibo.it. UBLCS Technical Report Series 93-15 Data Algorithm: A Numerical Method to Extract Shape Information from Gray Scale Images, R. Davoli, F. Tamburini, June 1993. 93-16 Towards Performance Evaluation in Process Algebras, R. Gorrieri, M. Roccetti, July 1993. 93-17 Split and ST Bisimulation Semantics, R. Gorrieri, C. Laneve, July 1993. 93-18 Multilanguage Interoperability, G. Attardi, M. Gaspari, July 1993. 93-19 HERMES: an Expert System for the Prognosis of Hepatic Diseases, I. Bonf a, C. Maioli, F. Sarti, G.L. Milandri, P.R. Dal Monte, September 1993. 93-20 An Information Flow Security Property for CCS, R. Focardi, R. Gorrieri, October 1993. 93-21 A Classification of Security Properties, R. Focardi, R. Gorrieri, October 1993. 93-22 Real Time Systems: A Tutorial, F. Panzieri, R. Davoli, October 1993. 93-23 A Sca...

This article presents a congruence format, in structural operational semantics, for rooted branching bisimulation equivalence. The format imposes additional requirements on Groote’s ntyft format. It extends an earlier format by Bloom with standard notions such as recursion, iteration, predicates, and negative premises. 1

ing from just the two atomic actions in I def = fthrow; tailg, FIR b 1 yields I ((throw tail) throw head) = head: First, observe I (throw tail) = . Then, using (4), it easily follows that I ((throw tail) throw head) = head: This expresses that head eventually comes up, and thus excludes the infinite sequence of -steps present in I ((throw tail) throw head). 7.2 Empty Process Let the symbol " denote the empty process, introduced as a unit for sequential composition by Koymans and Vrancken in [58] (see also [28, 74]). Obvious as " may be (being a unit for \Delta), its introduction is nontrivial because at the same time it must be a unit for k as well. In the design of BPA, PA, ACP and related axiom systems, it has proved useful to study versions of the theory, both with and without ". Just for this reason the star operation with its (original) defining equation as given by Kleene in [54] was introduced in process algebra. Taking y = " in x y, one obtains x ...

This paper shows that the collection of identities in two variables which hold in the algebra N of the natural numbers with constant zero, and binary operations of sum and maximum does not have a finite equational axiomatization. This gives an alternative proof of the non-existence of a finite basis for N - a result previously obtained by the authors. As an application of the main theorem, it is shown that the language of Basic Process Algebra (over a singleton set of actions), with or without the empty process, has no finite \omega-complete equational axiomatization modulo trace equivalence.

Abstract. We prove a unique decomposition theorem for a class of ordered commutative monoids. Then, we use our theorem to establish that every weakly normed process definable in ACP ε with bounded communication can be expressed as the parallel composition of a multiset of weakly normed parallel prime processes in exactly one way. 1

This paper explores the connection between semantic equivalences and preorders for concrete sequential processes, represented by means of labelled transition systems, and formats of transition system specications using Plotkin's structural approach. For several preorders in the linear time { branching time spectrum a format is given, as general as possible, such that this preorder is a precongruence for all operators speci- able in that format. The formats are derived using the modal characterizations of the corresponding preorders. 1. Introduction Structural operational semantics [24] provides process algebras and specication languages with an interpretation. It generates a (labelled) transition system in which states are the closed terms over a (single-sorted, rst-order) signature, and transitions between states may be supplied with labels. The transition relation is obtained from a transition system specication (TSS), this being a set of proof rules called transition rules. I...

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