Bernd Baumgarten

On internal and external characterizations of PT-net building block behavior

Subnets whose relative boundary consists only of transitions, termed building blocks, are used to structure specifications of distributed systems. In this paper we consider the problem how to determine the effects of a building block on its possible environments, considering only its internal structure. External equivalence of building blocks allows one to change these components without affecting the behaviour of the environment and is thus of practical importance. As there are infinitely many potential environments, external equivalence cannot be expressed in a finite form (nor proven) easily. We investigate contexts in which internal equivalence, which is often obtainable without too much effort, is a sufficient condition for external equivalence. The approach chosen here is to specify the building blocks internally by a set of net languages, and to define internal equivalence as the equality of these specifications.

The signing of a contract — a tree-structured application modelled with petri net building blocks

The desire to replace conventional forms of cooperation within organizational structures by computer services raises the necessity to model cooperation and to describe it formally.

Testability with Unbounded Testing Strategies

Testability and design for testability are widely discussed practical issues in software engineering, especially in protocol engineering. A number of basic testability qualities were defined formally and independently from any special system model. In this paper we refine these notions on the one hand by a containment order on experiments and on the other hand by a formal distinction between bounded and unbounded experimentation. Containment and bounds will be interpreted mainly temporally, but can also more generally be considered as referring to a “width of view”, of which time is only one, though prominent, aspect.

PR OSI T—an R&D project stimulated by the standardization work on open systems interconnection (OSI)

Abstract From its very beginning, GMD and in particular its former Institute for Teleprocessing in Darmstadt — which, in 1992, became the Institute for TeleCooperationTechnique — were heavily engaged in the standardization work on Open Systems Interconnection. In 1982, the institute decided to complement its OSI engagement by an R&D-project, called PROSIT. Its objective was to keep track of OSI progress and to develop, in response to fundamental questions posed there, a design methodology for cooperating systems. This paper gives an overview of PROSIT and its relationship to the standardization work on OSI. Particular emphasis is placed on the PROSIT approaches to system modelling in general, to formal protocol specification and analysis and to the generation of conformance tests. The relationship between PROSIT and OSI standardization serves as an example for the mutual benefits R&D and standardization work can provide to each other.

A Minimal Framework for Specification Theory

Notions concerning the specification, implementation, verification and testing of systems are ordinarily defined within a given context. We discuss what could and should belong to such a specification context. We obtain a unique practice-oriented specification semantics resp. conformance relation. We expect our framework to permit the definition of a general vocabulary for specification, verification and testing, independent of specific models or languages.

Testing of Communicating Systems

Academic research has made significant advances in the generation of test sequences from formal specifications and in the development of computer-aided test tools with the aims of improving the effectiveness of testing communicating systems. However, this state-of-the-art research is not necessarily the state-of-the-practice; these methods and tools are seldom used in the communications industry. As academia tends to work on problems that are not too industrially related and does not quite address the prohlems facing testers in the industry, testers generally regard academic testing techniques impractical and irrelevant to solving real problems. There is a big gap between testing practice and research results published in journals and reported at conferences. This paper argues that academic research on testing of communicating systems needs to become more industrially relevant, describes the means by which this change can be facilitated, and suggests some research topics that are relevant to the industry. It aims to help effect a change in the direction of academic research on testing of communicating systems.

Modeling and verification of a checkpoint-restart-protocol

The paper presents a protocol for the treatment of temporary local crashes and communication failures in systems of communicating processes. Assuming the existence of a global partitioning of the processes’ interactions into a sequence of segments as well as the availability of a reliable memory to each participant, the recovery strategy lies in the provident permanent recording and discarding of checkpoint data and, in cases of failure, common restarts from some recent global checkpoint (boundary between two segments). Apart from the inherent limitations imposed by data flow and resources the processes may run totally asynchronously. The protocol is modelled by a PrT-net, which permits to formally state and verify the protocol’s service, namely guaranteeing liveness and the eventual progress of the system’s actions. The final part of this paper is devoted to the structure and basic ideas of this proof.