A design model for Open Distributed Processing systems

This paper proposes design concepts that allow the conception, understanding and development of complex technical structures for open distributed systems. The proposed concepts are related to, and partially motivated by, the present work on Open Distributed Processing (ODP). As opposed to the current ODP approach, the concepts are aimed at supporting a design trajectory with several, related abstraction levels. Simple examples are used to illustrate the proposed concepts

Fieldbus technology in industrial automation

http://ieeexplore.ieee.org/Fieldbus technology in industrial automation is not only relatively complex because of the number of solutions possible, but also, and above all, because of the variety of applications. Ironically, these in turn are responsible for the multitude of solutions available. If the analysis of the basic needs is relatively standard, as they will always involve connecting sensors, actuators, and field controllers with each other, the options in architecture are numerous and can impose the need for certain services. The required performances themselves and the quality of service expected fundamentally depend on the applications. This article traces this technology from its beginnings, which go back to the first industrial networks in the 1970's. The principal stages of development are recounted, from the initial requirement specifications to the current state of international standardization. The diverse technical solutions are then analyzed and classified. In particular, we study the temporal aspects, the medium access control protocols and application relationships

Specification and verification issues in a process language

PhD ThesisWhile specification formalisms for reactive concurrent systems are now reasonably well-understood theoretically, they have not yet entered common, widespread design practice. This motivates the attempt made in this work to enhance the applicability of an important and popular formal framework: the CSP language, endowed with a failure-based denotational semantics and a logic for describing failures of processes. The identification of behaviour with a set of failures is supported by a convincing intuitive reason: processes with different failures can be distinguished by easily realizable experiments. But, most importantly, many interesting systems can be described and studied in terms of their failures. The main technique employed for this purpose is a logic in which process expressions are required to satisfy an assertion with each failure of the behaviour they describe. The theory of complete partial orders, with its elegant treatment of recursion and fixpoint-based verification, can be applied to this framework. However, in spite of the advantages illustrated, the practical applicability of standard failure semantics is impaired by two weaknesses. The first is its inability to describe many important systems, constructed by connecting modules that can exchange values of an infinite set across ports invisible to the environment. This must often be assumed for design and verification purposes (e.g. for the many protocols relying upon sequence numbers to cope with out-of-sequence received messages). Such a deficiency is due to the definition of the hiding operator in standard failure semantics. This thesis puts forward a solution based on an interesting technical result about infinite sets of sequences. Another difficulty with standard failure semantics is its treatment of divergence, the phenomenon in which some components of a system interact by performing an infinite, uninterrupted sequence of externally invisible actions. Within failure semantics, divergence cannot be abstracted from on the basis of the implicit fairness assumption that, if there is a choice leading out of divergence, it will eventually be made. This 'fair abstraction' is essential for the verification of many important systems, including communication protocols. The solution proposed in this thesis is an extended failure semantics which records refused traces, rather than just actions. Not only is this approach compatible with fair abstraction, but it also permits, like ordinary failure semantics, verification in a compositional calculus with fixpoint induction. Rather interestingly, these results can be obtained outside traditional fixpoint theory, which cannot be applied in this case. The theory developed is based on the novel notion of 'trace-based' process functions. These can be shown to possess a particular fixpoint that, unlike the least fixpoint of traditional treatments, is compatible with fair abstraction. Moreover, they form a large class, sufficient to give a compositional denotational semantics to a useful eSP-like process language. Finally, a logic is proposed in which the properties of a process' extended failures can be expressed and analyzed; the methods developed are applied to the verification of two example communication protocols: a toy one and a large case study inspired by a real transport protocol

Discrete Event Systems: Models and Applications; Proceedings of an IIASA Conference, Sopron, Hungary, August 3-7, 1987

Work in discrete event systems has just begun. There is a great deal of activity now, and much enthusiasm. There is considerable diversity reflecting differences in the intellectual formation of workers in the field and in the applications that guide their effort. This diversity is manifested in a proliferation of DEM formalisms. Some of the formalisms are essentially different. Some of the "new" formalisms are reinventions of existing formalisms presented in new terms. These "duplications" reveal both the new domains of intended application as well as the difficulty in keeping up with work that is published in journals on computer science, communications, signal processing, automatic control, and mathematical systems theory - to name the main disciplines with active research programs in discrete event systems. The first eight papers deal with models at the logical level, the next four are at the temporal level and the last six are at the stochastic level. Of these eighteen papers, three focus on manufacturing, four on communication networks, one on digital signal processing, the remaining ten papers address methodological issues ranging from simulation to computational complexity of some synthesis problems. The authors have made good efforts to make their contributions self-contained and to provide a representative bibliography. The volume should therefore be both accessible and useful to those who are just getting interested in discrete event systems