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W. Vogler

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4 papers

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TCS Journal 2006 Journal Article

Fairness of components in system computations

F. Corradini
M.R. Di Berardini
W. Vogler

In this paper we provide a simple characterization of (weak) fairness of components as defined by Costa and Stirling in [Weak and strong fairness in CCS, Inform. and Comput. 73 (1987) 207–244]. The study is carried out at system specification level by resorting to a common process description language. This paper follows and exploits similar techniques as those developed in [F. Corradini, M. R. Di Berardini, W. Vogler, Relating fairness and timing in process algebras, Proc. of Concur’03, Lecture Notes in Computer Science, Vol. 2761, Springer, Berlin, 2003, pp. 446–460]—where fairness of actions was taken into account and was contrasted to the PAFAS timed operational semantics—but the characterization of fair executions is based on a new semantics for PAFAS; it makes use of only two copies of each basic action instead of infinitely many as in [G. Costa, C. Stirling, Weak and strong fairness in CCS, Inform. and Comput. 73 (1987) 207–244] and allows for a simple and finite representation of fair executions by using regular expressions. The new semantics can also be understood as describing timed behaviour of systems with upper time bounds. The paper discusses in detail how this new semantics differs from the old one, and why theses changes are necessary to properly capture fairness of components.

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TCS Journal 2005 Journal Article

Measuring the performance of asynchronous systems with PAFAS

F. Corradini
W. Vogler

Based on Process Algebra for Faster Asynchronous Systems (PAFAS), a testing-based faster-than relation has previously been developed that compares the worst-case efficiency of asynchronous systems. This approach reveals that pipelining does not improve efficiency in general; that it does so in practice depends on assumptions about the user behaviour. As a case study for testing under such assumptions, we adapt the PAFAS-approach to a setting where user behaviour is known to belong to a specific, but often occurring class of request–response behaviours. Just as the testing preorder in classical testing, the original faster-than relation is qualitative. We give it a quantitative reformulation for the general approach; based on this, we demonstrate in our case study how to determine an asymptotic performance measure for finite-state processes. With this result, we can show that pipelining indeed improves efficiency in our setting, and we discuss additional examples.

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I&C Journal 1995 Journal Article

Generalized OM-Bisimulation

W. Vogler

History preserving bisimilarity and maximality preserving bisimilarity take full account of the interplay between causality and branching, and they are congruences w. r. t. action refinement for suitable classes of Petri nets. But even for finite safe Petri nets they are based on possibly infinite transition systems, and it is not obvious how to decide them. OM-bisimulation gives a characterization of history preserving bisimulation for safe nets without internal moves, and it allows a decidability result. In this paper we generalize OM-bisimulation and this decidability result to safe nets with internal moves, and also treat the case of maximality preserving bisimulation.

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I&C Journal 1995 Journal Article

Timed Testing of Concurrent Systems

W. Vogler

This paper is concerned with timing considerations for concurrent systems where the time needed by the individual actions is not known beforehand: it has long been suspected that the power of partial order semantics is needed here. We develop a suitable testing scenario to study this idea. With one view of timed behaviour, we can confirm that interval semiword semantics, a special partial order semantics, is indeed what can be observed with timed tests. With another view, our testing scenario leads to timed-refusal-trace semantics; this is a noninterleaving semantics, but it seems that it cannot be represented with partial orders in a meaningful way.

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