Scientific publications

Connected high-tech systems allow the gathering of operational data at unprecedented volumes. A direct benefit of this is the possibility to extract usage models, that is, a generic representations of how such systems are used in their field of application. Usage models are extremely important, as they can help in understanding the discrepancies between how a system was designed to be used and how it is used in practice.

IoT applications and other distributed control applications are characterized by the interaction of many hardware and software components. The inherent complexity of the distributed functionality introduces challenges on the detection and correction of issues related to functionality or performance, which are only possible to do after system prototypes or pilot installations have been built.

The complexity of cyber-physical systems is increasing, driven by integration of more functionality and trends towards mass-customization. This has resulted in complex systems with many variants that require long time to develop and are difficult to adapt to changing requirements and introduction of new technology.

Kahn and MacQueen have introduced a generic class of determinate asynchronous data-flow applications, called Kahn Process Networks (KPNs) with an elegant mathematical model and semantics in terms of Scott-continuous functions on data streams together with an implementation model of independent asynchronous sequential programs communicating through FIFO buffers with blocking read and non-blocking write operations.

More and more high tech companies are struggling with the maintenance of legacy software. Legacy software is vital to many organizations, so even if its behavior is not completely understood it cannot be thrown away. To re-factor or re-engineer the legacy software components, the external behavior needs to be preserved after replacement so that the replaced components possess the same behavior in the system environment as the original components.

The IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) protocol defines two types of timeslots for communications, namely dedicated and shared timeslots. An upper layer in the protocol stack uses these timeslots to design a communication schedule for the network links, based on the required bandwidth for each link.

When software components are developed iteratively, code frequently evolves in an inductive manner: A unit is created and is then copied and modified many times. Such development often happens when variation points and, hence, proper domain abstractions are initially unclear. As a result, there may be substantial amounts of code duplication, and the code may be difficult to understand and maintain, warranting a redesign.

Energy efficiency is of paramount importance in designing low-power wireless sensor nodes. Approximate computing is a new circuit-level technique for reducing power consumption. However, the gain in power by applying this technique is achieved at the cost of computational errors. The impact of such inaccuracies in the circuit level of a radio transceiver chip on the performance of Wireless Sensor Networks has not yet been explored.

Cyber-physical systems consist of many hardware and software components. Over the life-cycle of these systems, components are replaced or updated. To avoid integration problems, good interface descriptions are crucial for component-based development of these systems. For new components, a Domain Specific Language called Component Modeling Analysis can be used to formally define the interface of such a component in terms of its signature, state and timing behavior.

In multi-media applications, bufers represent storage spaces that are used to store the data communicated between diferent tasks in the application, and throughput refers to the rate at which output data is produced by the application. The capacities of the bufers inluence the throughput, by altering the waiting times for tasks that need to read or write data from or to the bufers.