Scientific publications

A system functions as part of a broader enterprise. For the design of a system understanding is required of its purpose within the enterprise, as well as of its internal functioning. Models are a means to create and capture understanding. Many different models are needed during the design of a system, from broad enterprise models down to detailed implementation models of components or functions.

In this paper, the stability of a Networked Control System (NCS) with time-varying delays is analyzed. A discretetime state-space model is used to analyze the dynamics of the NCS. The delay is introduced by the network itself and is assumed to be upperbounded by a fraction of the sample-time. A typical motion control example is presented in which the timevariation of the delay results in an unstable system, although for each fixed delay the system is stable.

Since testing is inherently incomplete, test selection is of vital importance. Coverage measures evaluate the quality of a test suite and help the tester select test cases with maximal impact at minimum cost. Existing coverage criteria for test suites are usually defined in terms of syntactic characteristics of the implementation under test or its specification.

In the past decades, many formal frameworks (e.g. timed automata and temporal logics) and techniques (e.g. model checking and theorem proving) have been proposed to model a real-time system and to analyze real-time properties of the model. However, due to the existence of ineliminable timing differences between the model and its realization, real-time properties verified in the model often cannot be preserved in itsrealization.

The complexity of real-time embedded systems is increasing, for example due to the use of distributed architectures. An extension to the Vienna Development Method (VDM) is proposed to address the problem of deployment of software on distributed hardware. The limitations of the current notation are discussed and new language elements are introduced to overcome these deficiencies.

Soft real-time systems are often analysed using hard realtime techniques, which are not suitable to take into account the deadline misses rate allowed in such systems. Therefore, the resulting system is over-dimensioned, thus expensive. To appropriately dimension soft real-time systems, adequate models, capturing their varying runtime behaviour, are needed.

In 2005, Stevens Institute of Technology’s System Design and Operational Effectiveness (SDOE) Program added audio lectures to their online Fundamentals of Systems Engineering course. This paper compares results from four instantiations of this online course with no audio lectures delivered in 2004 to results from three instantiations of the same online course with audio lectures delivered in 2005.