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Discrete-event (DE) models are formal system specifications that have analyzable deterministic behaviors. Using a global, consistent notion of time, DE components communicate via time-stamped events. DE models have primarily been used in performance modeling and simulation, where time stamps are a modeling property bearing no relationship to real time during execution of the model. In this paper, we extend DE models with the capability of relating certain events to physical time. We propose a programming model, called PTIDES (Programming Temporally Integrated Distributed Embedded Systems), which has DE semantics, but with carefully chosen relations between model time and real time. Key to making this model effective is to ensure that constraints that guarantee determinacy in the semantics are preserved at runtime. To accomplish this, we give a distributed execution strategy that obeys DE semantics without the penalty of totally ordered executions based on time stamps. Our technique relies on having a distributed common notion of time, known to some precision. Based on causality analysis of DE models, we define relevant dependency and relevant orders to enable out-of-order execution without compromising determinism and without requiring backtracking. 1

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Reo is a coordination model based on circuit-like connectors which coordinate components through the interplay of data flow, synchronisation and mutual exclusion, state, and context-dependent behaviour. This paper proposes a scheme based on connector colouring for determining the behaviour of a Reo connector by resolving its context dependent synchronisation and mutual exclusion constraints. Colouring a Reo connector in a specific state with given boundary conditions (I/O requests) provides a means to determine the routing alternatives for data flow. Our scheme has the advantage over previous models in that it is simpler to implement and that it models Reo connectors more closely to their envisaged semantics than existing formal models.

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Abstract. This paper argues that basing the semantics of concurrent systems on the notions of state and state transitions is neither advisable nor necessary. The tendency to do this is deeply rooted in our notions of computation, but these roots have proved problematic in concurrent software in general, where they have led to such poor programming practice as threads. I review approaches (some of which have been around for some time) to the semantics of concurrent programs that rely on neither state nor state transitions. Specifically, these approaches rely on a broadened notion of computation consisting of interacting components. The semantics of a concurrent compositions of such components generally reduces to a fixed point problem. Two families of fixed point problems have emerged, one based on metric spaces and their generalizations, and the other based on domain theories. The purpose of this paper is to argue for these approaches over those based on transition systems, which require the notion of state. 1

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2.1 Synchronous Systems....................................... 4 2.1.1 STS and FSTS...................................... 4