In the semantics of programming, nite data types such as finite lists, have traditionally been modelled by initial algebras. Later final coalgebras were used in order to deal with in finite data types. Coalgebras, which are the dual of algebras, turned out to be suited, moreover, as models for certain types of automata and more generally, for (transition and dynamical) systems. An important property of initial algebras is that they satisfy the familiar principle of induction. Such a principle was missing for coalgebras until the work of Aczel (Non-Well-Founded sets, CSLI Leethre Notes, Vol. 14, center for the study of Languages and information, Stanford, 1988) on a theory of non-wellfounded sets, in which he introduced a proof principle nowadays called coinduction. It was formulated in terms of bisimulation, a notion originally stemming from the world of concurrent programming languages. Using the notion of coalgebra homomorphism, the definition of bisimulation on coalgebras can be shown to be formally dual to that of congruence on algebras. Thus, the three basic notions of universal algebra: algebra, homomorphism of algebras, and congruence, turn out to correspond to coalgebra, homomorphism of coalgebras, and bisimulation, respectively. In this paper, the latter are taken

Groote and Vaandrager introduced the tyft/tyxt format for Transition System Specifications (TSSs), and established that for each TSS in this format that is well-founded, the bisimulation equivalence it induces is a congruence. In this paper, we construct for each TSS in tyft/tyxt format an equivalent TSS that consists of tree rules only. As a corollary we can give an affirmative answer to an open question, namely whether the well-foundedness condition in the congruence theorem for tyft/tyxt can be dropped. These results extend to tyft/tyxt with negative premises and predicates. 1

We set up a formal framework to describe transition system specifications in the style of Plotkin. This framework has the power to express many-sortedness, general binding mechanisms and substitutions, among other notions such as negative hypotheses and unary predicates on terms. The framework is used to present a conservativity format in operational semantics, which states sufficient criteria to ensure that the extension of a transition system specification with new transition rules does not affect the semantics of the original terms.

Abstract not found

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...

Abstract not found

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

We set up a formal framework to describe term deduction systems, such as transition system speci cations in the style of Plotkin, and conditional term rewriting systems. This framework has the power to express many-sortedness, general binding mechanisms and substitutions, among other notions such as negative premises and unary predicates on terms. The framework is used to present a conservativity format in operational semantics, which states su cient criteria to ensure that the extension of a transition system speci cation with new rules does not a ect the behaviour of the original terms. Furthermore, we showhowgeneral theorems in structured operational semantics can be transformed into results in conditional term rewriting. We apply this approach to the conservativity theorem, which yields a result that is useful in the eld of abstract data types. 1

We transpose a conservative extension theorem from structural operational semantics to conditional term rewriting. The result is useful for the development of software renovation factories, and for modular specification of abstract data types.

Abstract. This paper presents a method for the decomposition of HML formulae. It can be used to decide whether a process algebra term satisfies a HML formula, by checking whether subterms satisfy certain formulae, obtained by decomposing the original formula. The method uses the structural operational semantics of the process algebra. The main contribution of this paper is that an earlier decomposition method from Larsen [14] for the De Simone format is extended to the more general ntyft/ntyxt format without lookahead. 1