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We present real time and discrete time versions of ACP with absolute timing and relative timing. The starting-point isanewrealtimeversion with absolute timing, called ACPsat, featuring urgent actions and a delay operator. The discrete time versions are conservative extensions of the discrete time versions of ACP being known as ACP dat and ACP drt. The principal version is an extension of ACP sat with integration and initial abstraction to allow for choices over an interval of time and relative timing to be expressed. Its main virtue is that it generalizes ACP without timing and most other versions of ACP with timing in a smooth and natural way. This is shown for the real time version with relative timing and the discrete time version with absolute timing.

The aim of this paper is to nd the nest `observable ' and `implementable' equivalence on concurrent processes. This is a part of a larger programme to develop a theory of observable processes where semantics of processes are based on locally and nitely observable process behaviour, and all process constructs are allowed, provided their operational meaning is de ned by realistically implementable transition rules.

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Several high-level programming languages for programming agents and robots have been proposed in recent years. Each of these languages has its own features and merits. It is still difficult, however, to compare different programming frameworks and evaluate the relative benefits and disadvantages of these frameworks. In this paper, we present a general method for comparing agent programming frameworks based on a notion of bisimulation, and use it to formally compare the languages ConGolog and 3APL. ConGolog is a concurrent language for high-level robot programming based on the situation calculus. ConGolog provides a logical perspective on robot programming, but also incorporates a number of imperative programming constructs like sequential composition. 3APL is an agent programming language and its semantics offers a more operational perspective on agents. The language is a combination of logic and imperative programming and provides operators for beliefs, goals and plans of an ag...

JavaSpaces and TSpaces are two coordination middlewares for distributed Java programming recently proposed by Sun and IBM, respectively. They extend the data-driven coordination model of Linda with an event notification mechanism: a process can register interest in the incoming arrivals of a particular kind of data and receive communication of the occurrences of these events. In [2, 3] we introduce a process calculus L, based on the Linda coordination model, and we prove that if processes are synchronous with the dataspace (ordered interpretation) L is Turing powerful, while this is not the case if they are asynchronous (unordered interpretation). Here, we introduce a new calculus Ln , obtained by extending L with the event noti cation mechanism, and we prove two main results contrasting with what has been shown for L: (i) Ln is Turing powerful also under the unordered interpretation and (ii) it allows a faithful encoding of the ordered semantics on top of the unordered one.

In this paper we present an algebraic language for the specification of probabilistic and nondeterministic processes, PNAL, which is a probabilistic extension of EPL (Algebraic Theory of Processes, M. Hennessy) that maintains nondeterminism.

We present a process algebra expressing probabilistic external/internal choices, multi-way synchronizations, and processes with dierent advancing speeds in the context of discrete time, i.e. where time is not continuous but is represented by a sequence of discrete steps as in Discrete Time Markov Chains (DTMCs). To this end, we introduce a variant of CSP that employs a probabilistic asynchronous parallel operator whose synchronization mechanism is based on a mixture of the classical generative and reactive models of probability. In particular, dierently from existing discrete time process algebras, where parallel processes are executed in synchronous locksteps, the parallel operator that we adopt allows processes with dierent probabilistic advancing speeds (mean number of actions executed per time unit) to be modeled. Moreover, our generative-reactive synchronization mechanism makes it possible to always derive DTMCs in the case of fully specied systems. We then present a sound and complete axiomatization of probabilistic bisimulation over - nite processes of our calculus, that is a smooth extension of the axiom system for a standard process algebra, thus solving the open problem of cleanly axiomatizing action restriction in the generative model. As a further result, we show that, when evaluating steady state based performance measures which are expressible by attaching rewards to actions, our approach provides an exact solution even if the advancing speeds are considered not to be probabilistic, without incurring the state space explosion problem that arises with standard synchronous approaches. We - nally present a case study on multi-path routing showing the expressiveness of our calculus and that it makes it particularly easy to produce scalable specications....

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...

. We propose a ve-valued logic that can be motivated from an algorithmic point of view and from a logical perspective. This logic is combined with process algebra. For process algebra with ve-valued logic we present an operational semantics in SOS-style and a completeness result. Finally, we discuss some generalizations. Key words & Phrases: Concurrency, process algebra, many-valued logic, conditional guard construct, conditional composition. 1991 CR Categories: F.3, F.4.3, I.1. 1 Introduction Assume P is some simple program or algorithm. Then the initial behaviour of if then P else P depends on evaluation of the condition : either it yields an immediate error, or it starts performing P , or it diverges in evaluation of . Note that the second possibility only requires that is either true or false. The following three nonclassical truth values accommodate these intuitions: Meaningless. Typical examples are errors that are detectable during execution such as a type-clash or...