Invited Talks & Accepted Papers

We consider the model of Generative Probabilistic Transition Systems, and Baier and Hermanns' notion of weak bisimulation defined over them. We prove that, if we consider any process algebra giving rise to a Generative Probabilistic Transition System satisfying the condition of regularity and offering prefixing, interleaving, and guarded recursion, then the coarsest congruence that is contained in weak bisimulation is strong bisimulation.

RCCS is a variant of Milner's CCS where processes are allowed a controlled form of backtracking. It turns out that the RCCS reinterpretation of a CCS process is equivalent, in the sense of weak bisimilarity, to its causal transition system in CCS. This can be used to develop an efficient method for designing distributed algorithms, which we illustrate here by deriving a distributed algorithm for assembling trees. Such a problem requires solving a highly distributed consensus, and a comparison with a traditional CCS-based solution shows that the code we obtain is shorter, easier to understand, and easier to prove correct by hand, or even to verify.

In the context of process algebras it is customary to define semantics in the form of a reaction relation supported by a structural congruence relation. Recently process algebras have grown more expressive in order to meet the modelling demands of fields as diverse as business modelling and systems biology. This leads to combining various features, such as general choice and parallelism that were previously studied separately, and it often becomes difficult to define the reaction semantics. We present a general approach based on Active Evaluation Contexts that allows the reaction semantics to be easily constructed.

Strategies are a powerful mechanism to control rule application in rule-based systems. For instance, different transition relations can be defined and then combined by means of strategies, giving rise to an effective tool to define the semantics of programming languages. We have endowed the Maude MSOS Tool (MMT), an executable environment for modular structural operational semantics, with the possibility of defining strategies over its transition rules, by combining MMT with the Maude strategy language interpreter prototype. The combination was possible due to Maude's reflective capabilities. One possible use of MMT with strategies is to execute Ordered SOS specifications. We show how a particular form of strategy can be defined to represent an OSOS order and therefore execute, for instance, SOS specifications with negative premises. In this context, we also discuss how two known techniques for the representation of negative premises in OSOS become simplified in our setting.

In this paper, we solve two open problems posed by Karen L. Bernstein regarding her promoted tyft format for structured operational semantics. We show that, unlike formats with closed terms as labels, such as the tyft format, the well-foundedness assumption cannot be dropped for the promoted tyft format while preserving the congruence result. We also show that the well-founded promoted tyft format is incomparable to the tyft format with closed terms as labels, i.e., there are transition relations that can be specified by the promoted tyft format but not by the tyft format, and vice versa.

The Structural Operational Semantics Development Tooling (SOSDT) Eclipse Plugin integrates the Relational Meta-Language (RML) compiler and debugger with the Eclipse Integrated Development Environment Framework. SOSDT, together with the RML compiler and debugger, provides an environment for developing and maintaining executable Structural Operational Semantics specifications, including the Natural Semantics big step variant of SOS specifications. The RML language is successfully used at our department for writing large specifications for a range of languages like Java, Modelica, Pascal, MiniML etc. The SOSDT environment includes support for browsing, code completion through menus or popups, code checking, automatic indentation, and debugging of specifications.