Open Estelle

Introduction

Estelle [ISO97] specifications describe systems of communicating components (module instances). The specified system is closed, i.e. it has no ability to interact with some environment. Because of this restriction, open systems can only be specified together with and incorporated with an environment.
To overcome this restriction, we introduce a compatible extension of Estelle, called "Open Estelle". It allows the specification of (topologically) open systems, i.e. systems that have the ability to communicate with any environment through a well-defined external interface. We define a formal syntax and a formal semantics for Open Estelle, both based on and extending the syntax and semantics of Estelle. The extension is compatible syntactically and semantically, i.e. Estelle is a subset of Open Estelle. In particular, the formal semantics of Open Estelle reduces to the Estelle semantics in the special case of a closed system.
A detailed introduction to Open Estelle can be found in [ThGo98b]

Language Definition

A formal definition of Open Estelle can be found in [ThGo97c].

Tools and Implementations

To create a platform for practical experiments, we have developed a tool set for the processing of Open Estelle sources. The front end of this tool set is a compiler that translates Open Estelle sources (i.e. interfaces, specifications, and behaviour-definitions) into a binary intermediate form, which can be processed by the other tools. This front end was developed out of the existing Estelle compiler front-end PET ("Portable Estelle Translator", [SiSt93]).
The toolset also includes XEC, a compiler for the creation of efficient implementations of open systens. A prelaminary version of this tools may be requested from the authors.

Literature

Publications

[GoRoTh96]	R. Gotzhein, F. Rößler, J. Thees: Towards Open Estelle in: U. Herzog, H. Hermanns (Hrsg.): Formale Beschreibungstechniken für verteilte Systeme, Proceedings des 6. GI/ITG-Fachgesprächs, Erlangen, 20.-21.6.1996, pp. 89-98
[ThGo97c]	J. Thees, R. Gotzhein: A Formal Syntax and a Formal Semantics for Open Estelle Internal Report No. 292/97, Dept. of Comp. Sci., University of Kaiserslautern, 1997
[ThGo97e]	J. Thees, R. Gotzhein: Open Estelle - A Formal Description Technique for Open Distributed Systems International Workshop on Dynamic Modeling of Information Systems, Yamagata, Japan, November 1997
[ThGo98b]	J. Thees, R. Gotzhein: Open Estelle - An FDT for Open Distributed Systems in: S. Budkowski, A, Cavalli, E. Najm (Edts.): Formal Destcription Techniques and Protocol Specification, Testing and Verification (FORTE XI/PSTV XVIII'98), Kluwer Academic Publishers, Boston/Dordrect/London, 1998

External References

[ISO97] ISO/TC97/SC21: Estelle - A Formal Description Technique Based on an Extended State Transition Model,
ISO/TC97/SC21, IS 9074, 1997

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