Techn. Hochsch., Diss., 2003--Aachen.

Techn. University, Diss., 2005--Darmstadt.

In die Infrastruktur unserer Gesellschaft sind komplexe IT-Systeme fest eingebettet. Die Verbreitung und Verstetigung von IT-Systemen betrifft zentrale Bereiche unserer Gesellschaft beispielsweise Verkehrs-, Finanz- oder Gesundheitssystem. Lange Zeit standen funktionale Aspekte bei der Entwicklung informationstechnischer Systeme im Vordergrund. In den letzten Jahren haben sich jedoch nichtfunktionale Eigenschaften von IT-Systemen wie Robustheit zu unverzichtbaren Schlüsseleigenschaften in einer Vielzahl von Anwendungsfeldern entwickelt. Systeme während der Betriebsphase sind Veränderungen der gegebenen Einsatz- und Betriebsbedingungen durch Störungen der Umgebung oder auch Verschleißerscheinungen ausgesetzt. Ziel der Forschungsarbeit ist es ein Konzept für die Systemeigenschaft Robustheit zu entwickeln. Für ein gegebenes System mit einem definierten Funktionsziel ist zu analysieren, inwieweit es robust hinsichtlich Störungen der Einsatzbedingungen, verursacht durch Ereignisse der Umgebung, ist und folglich trotzdem das Funktionsziel erfüllt. Das vorgestellte Konzept umfasst dabei zwei wesentliche Problemstellungen: Bewertung der Robustheit Methode für robuste Systeme zur Laufzeit In Abhängigkeit der technischen Kennzahl, Robustheit, wird eine optimale Entscheidungsstrategie gewählt und so das Systemverhalten gesteuert. Mit der Integration eines Robustheitskonzepts insbesondere für den Systembetrieb soll anhand der Berücksichtigung der Systemeigenschaft Robustheit zur Laufzeit ein Beitrag zum Qualitätszuwachs bei Systemen geleistet werden. / Complex IT-systems are deeply embedded in the infrastructure of the society. The integration of these systems is important for plenty of areas such as the transportation system, the financial system or the health care system. For a long time, the functional aspects of the invention had been put forward. But lately the non-functional characteristics of IT-systems such as robustness have developed to essential key factors in many fields. A lot of systems are being exposed to environmental disturbances are showing during the stage of operation. This research work purpose is to develop a concept of robustness to increase system robustness. The robustness of embedded systems is supposed to be analyzed towards disturbances and terms of usage that were caused by the environment. Thereby the concept targets two main issues: measurement of the robustness and methods for robust systems concerning its duration. Depending on the value of robustness a proper decision is made in order to control the behavior of the system. Through an integration of the above mentioned concept, a rise of quality regarding the robustness of the system is pursued respecting its period of operation.

In die Infrastruktur unserer Gesellschaft sind komplexe IT-Systeme fest eingebettet. Die Verbreitung und Verstetigung von IT-Systemen betrifft zentrale Bereiche unserer Gesellschaft beispielsweise Verkehrs-, Finanz- oder Gesundheitssystem. Lange Zeit standen funktionale Aspekte bei der Entwicklung informationstechnischer Systeme im Vordergrund. In den letzten Jahren haben sich jedoch nichtfunktionale Eigenschaften von IT-Systemen wie Robustheit zu unverzichtbaren Schlüsseleigenschaften in einer Vielzahl von Anwendungsfeldern entwickelt. Systeme während der Betriebsphase sind Veränderungen der gegebenen Einsatz- und Betriebsbedingungen durch Störungen der Umgebung oder auch Verschleißerscheinungen ausgesetzt. Ziel der Forschungsarbeit ist es ein Konzept für die Systemeigenschaft Robustheit zu entwickeln. Für ein gegebenes System mit einem definierten Funktionsziel ist zu analysieren, inwieweit es robust hinsichtlich Störungen der Einsatzbedingungen, verursacht durch Ereignisse der Umgebung, ist und folglich trotzdem das Funktionsziel erfüllt. Das vorgestellte Konzept umfasst dabei zwei wesentliche Problemstellungen: Bewertung der Robustheit und Methode für robuste Systeme zur Laufzeit. In Abhängigkeit der technischen Kennzahl, Robustheit, wird eine optimale Entscheidungsstrategie gewählt und so das Systemverhalten gesteuert. Mit der Integration eines Robustheitskonzepts insbesondere für den Systembetrieb soll anhand der Berücksichtigung der Systemeigenschaft Robustheit zur Laufzeit ein Beitrag zum Qualitätszuwachs bei Systemen geleistet werden. / Complex IT-systems are deeply embedded in the infrastructure of the society. The integration of these systems is important for plenty of areas such as the transportation system, the financial system or the health care system. For a long time, the functional aspects of the invention had been put forward. But lately the non-functional characteristics of IT-systems such as robustness have developed to essential key factors in many fields. A lot of systems are being exposed to environmental disturbances are showing during the stage of operation. This research work purpose is to develop a concept of robustness to increase system robustness. The robustness of embedded systems is supposed to be analyzed towards disturbances and terms of usage that were caused by the environment. Thereby the concept targets two main issues: measurement of the robustness and methods for robust systems concerning its duration. Depending on the value of robustness a proper decision is made in order to control the behavior of the system. Through an integration of the above mentioned concept, a rise of quality regarding the robustness of the system is pursued respecting its period of operation.

For the reliability design of Engine Control Unit devices in motor vehicles, the knowledge of stresses occurring in the field within the product service life is essential. In addition to the environmental influences such as temperature, moisture and humidity, vibration and shock issues are in focus. To ensure the robustness of the products and they are still easily and inexpensively made, they must be interpreted appropriately in the development process. For this, the load spectra for the mechanical influences of road conditions and operating conditions are to be determined. Work will also include temperature and humidity values examined on typical installation locations. The essential everyday situations (commuters, taxi, farmer, ...) should be considered. Existing measurement technology must be combined to this end a comprehensive logger system with communication to the vehicle.

Living organisms throughout evolution have developed desired properties, such as the ability of maintaining functionality despite changes in the environment or their inner structure, the formation of functional modules, from metabolic pathways to organs, and most essentially the capacity to adapt and evolve in a process called natural selection. It can be observed in the metabolic networks of modern organisms that many key pathways such as the citric acid cycle, glycolysis, or the biosynthesis of most amino acids are common to all of them. Understanding the evolutionary mechanisms behind this development of complex biological systems is an intriguing and important task of current research in biology as well as artificial life. Several competing hypotheses for the formation of metabolic pathways and the mecha- nisms that shape metabolic networks have been discussed in the literature, each of which finds support from comparative analysis of extant genomes. However, while being powerful tools for the investigation of metabolic evolution, these traditional methods do not allow to look back in evolution far enough to the time when metabolism had to emerge and evolve to the form we can observe today. To this end, simulation studies have been introduced to discover the principles of metabolic evolution and the sources for the emergence of metabolism prop- erties. These approaches differ considerably in the realism and explicitness of the underlying models. A difficult trade-off between realism and computational feasibility has to be made and further modeling decisions on many scales have to be taken into account, requiring the combination of knowledge from different fields such as chemistry, physics, biology and last but not least also computer science. In this thesis, a novel computational model for the in silico evolution of early metabolism is introduced. It comprises all the components on different scales to resemble a situation of evolving metabolic protocells in an RNA-world. Therefore, the model contains a minimal RNA-based genetics and an evolving metabolism of catalytic ribozymes that manipulate a rich underlying chemistry. To allow the metabolic organization to escape from the confines of the chemical space set by the initial conditions of the simulation and in general an open- ended evolution, an evolvable sequence-to-function map is used. At the heart of the metabolic subsystem is a graph-based artificial chemistry equipped with a built-in thermodynamics. The generation of the metabolic reaction network is realized as a rule-based stochastic simulation. The necessary reaction rates are calculated from the chemical graphs of the reactants on the fly. The selection procedure among the population of protocells is based on the optimal metabolic yield of the protocells, which is computed using flux balance analysis. The introduced computational model allows for profound investigations of the evolution of early metabolism and the underlying evolutionary mechanisms. One application in this thesis is the study of the formation of metabolic pathways. Therefore, four established hypothe- ses, namely the backwards evolution, forward evolution, patchwork evolution and the shell hypothesis, are discussed within the realms of this in silico evolution study. The metabolic pathways of the networks, evolved in various simulation runs, are determined and analyzed in terms of their evolutionary direction. The simulation results suggest that the seemingly mutually exclusive hypotheses may well be compatible when considering that different pro- cesses dominate different phases in the evolution of a metabolic system. Further, it is found that forward evolution shapes the metabolic network in the very early steps of evolution. In later and more complex stages, enzyme recruitment supersedes forward evolution, keeping a core set of pathways from the early phase. Backward evolution can only be observed under conditions of steady environmental change. Additionally, evolutionary history of enzymes and metabolites were studied on the network level as well as for single instances, showing a great variety of evolutionary mechanisms at work. The second major focus of the in silico evolutionary study is the emergence of complex system properties, such as robustness and modularity. To this end several techniques to analyze the metabolic systems were used. The measures for complex properties stem from the fields of graph theory, steady state analysis and neutral network theory. Some are used in general network analysis and others were developed specifically for the purpose introduced in this work. To discover potential sources for the emergence of system properties, three different evolutionary scenarios were tested and compared. The first two scenarios are the same as for the first part of the investigation, one scenario of evolution under static conditions and one incorporating a steady change in the set of ”food” molecules. A third scenario was added that also simulates a static evolution but with an increased mutation rate and regular events of horizontal gene transfer between protocells of the population. The comparison of all three scenarios with real world metabolic networks shows a significant similarity in structure and properties. Among the three scenarios, the two static evolutions yield the most robust metabolic networks, however, the networks evolved under environmental change exhibit their own strategy to a robustness more suited to their conditions. As expected from theory, horizontal gene transfer and changes in the environment seem to produce higher degrees of modularity in metabolism. Both scenarios develop rather different kinds of modularity, while horizontal gene transfer provides for more isolated modules, the modules of the second scenario are far more interconnected.

Data stream processing in the industrial as well as in the academic field has gained more and more importance during the last years. Consider the monitoring of industrial processes as an example. There, sensors are mounted to gather lots of data within a short time range. Storing and post-processing these data may occasionally be useless or even impossible. On the one hand, only a small part of the monitored data is relevant. To efficiently use the storage capacity, only a preselection of the data should be considered. On the other hand, it may occur that the volume of incoming data is generally too high to be stored in time or–in other words–the technical efforts for storing the data in time would be out of scale. Processing data streams in the context of this thesis means to apply database operations to the stream in an on-the-fly manner (without explicitly storing the data). The challenges for this task lie in the limited amount of resources while data streams are potentially infinite. Furthermore, data stream processing must be fast and the results have to be disseminated as soon as possible. This thesis focuses on the latter issue. The goal is to provide a so-called Quality-of-Service (QoS) for the data stream processing task. Therefore, adequate QoS metrics like maximum output delay or minimum result data rate are defined. Thereafter, a cost model for obtaining the required processing resources from the specified QoS is presented. On that basis, the stream processing operations are scheduled. Depending on the required QoS and on the available resources, the weight can be shifted among the individual resources and QoS metrics, respectively. Calculating and scheduling resources requires a lot of expert knowledge regarding the characteristics of the stream operations and regarding the incoming data streams. Often, this knowledge is based on experience and thus, a revision of the resource calculation and reservation becomes necessary from time to time. This leads to occasional interruptions of the continuous data stream processing, of the delivery of the result, and thus, of the negotiated Quality-of-Service. The proposed robustness concept supports the user and facilitates a decrease in the number of interruptions by providing more resources.

Zugl.: Erlangen, Nürnberg, Univ., Diss., 2005

Zugl.: Zürich, Techn. Hochsch., Diss., 2006

Zugl.: Aachen, Techn. Hochsch., Diss., 2010.