004 Datenverarbeitung; Informatik
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- Doctoral Thesis (48) (remove)
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- Software Engineering (4)
- Information Retrieval (3)
- model-based (3)
- Abduktion <Logik> (2)
- Maschinelles Lernen (2)
- Modellgetriebene Entwicklung (2)
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This Thesis contributes by reporting on the current state of diffusion of collaboration information technology (CIT). The investigation concludes, with a high degree of certainty, that today we have a "satisfactory" diffusion level of some level-A CITs (mostly e-Mail, distantly followed by Audio Conferencing), and a "dissatisfactory" diffusion level of higher-level CITs (i.e. those requiring significant collaboration and cooperation among users, like Meeting Support Systems, Group Decision Support Systems, etc.). The potential benefits of the latter seem to be far from fully realised due to lack of user acceptance. This conclusion has gradually developed along the research cycle " it was suggested by Empirical Study I, and tested through Empirical Studies II and III. An additional, unplanned and rather interesting, finding from this study has been the recognition of large [mostly business] reporting on numerous Web 2.0 user-community produced collaboration technologies (most of them belonging to the category of "social software") and their metamorphosis from autonomous, "bottom-up" solutions into enterprise-supported infrastructures. Another contribution of this Thesis " again suggested by Empirical Study I, and tested through Empirical Studies II and III " pertains to the "process structure" of CIT diffusion. I have found that collaboration technology has historically diffused following two distinct (interdependent but orthogonal) diffusion paths " top-down (authority-based) and bottom-up. The authority-based diffusion path seems to be characterised by efforts aimed at "imposing" technologies on employees, the primary concern being to make sure that technology seamlessly and easily integrates into the organisational IT infrastructure. On the other hand, the bottom-up diffusion trail seems to be successful. The contribution of this investigation may be summarised as threefold: 1. This investigation consolidates most of the findings to date, pertaining to CIT adoption and diffusion, which have been produced by the CIT research community. Thus, it tells a coherent story of the dynamics of the community focus and the collective wisdom gathered over a period of (at least) one decade. 2. This work offers a meaningful framework within which to analyse existing knowledge " and indeed extends that knowledge base by identifying persistent problems of collaboration technology acceptance, adoption and diffusion. These problems have been repeatedly observed in practice, though the pattern does not seem to have been recognised and internalised by the community. Many of these problems have been observed in cases of CIT use one decade ago, five years ago, three years ago, and continue to be observed today in structurally the same form despite what is unarguably "rapid technological development". This gives me reason to believe that, at least some of the persistent problems of CIT diffusion can be hypothesised as "determining factors". My contribution here is to identify these factors, discuss them in detail, and thus tackle the theme of CIT diffusion through a structured historical narrative. 3. Through my contribution (2) above, I characterise a "knowledge-action gap" in the field of CIT and illuminate a potential path through which the research community might hope to bridge this gap. The gap may be operationalised as cognitive distance between CIT "knowledge" and CIT "action".
Within this thesis time evaluated predicate/transition nets (t-pr/t-nets) have been developed for the purpose to model, simulate and verify complex real-time systems. Therefore, t-pr/t-nets integrate concepts to model timing constraints and can be analysed by the means of structural analysis such as the calculation of s- and t-invariants as well as the identification of traps and co-traps. The applicability of t-pr/t-nets to model, simulate and verify complex systems in the domain of safety-critical real-time systems is proven by the Earliest-Deadline-First-Protocol (EDF) and the Priority-Inheritance-Protocol (PIP). Therefore, the EDF and PIP are modeled by means of t-pr/t-nets. The resulting t-pr/t-nets are verified using structural analysis methods. Due to the enormous complexity and the applicability of structural analysis methods for the verification of the EDF and PIP, it can be shown that t-pr/t-nets are appropriate to model, simulate and verify complex systems in the field of safety-critical real-time systems.
This thesis focuses on the utilization of modern graphics hardware (GPU) for visualization and computation purposes, especially of volumetric data from medical imaging. The considerable increase in raw computing power in recent years has turned commodity systems into high-performance workstations. In combination with the direct rendering capabilities of graphics hardware, "visual computing" and "computational steering" approaches on large data sets have become feasible. In this regard several example applications and concepts such as the "ray textures" have been developed and are discussed in detail. As the amount of data to be processed and visualized is steadily increasing, memory and bandwidth limitations require compact representations of the data. While the compression of image data has been investigated extensively in the past, the thesis addresses possibilities of performing computations directly on the compressed data. Therefore, different categories of algorithms are identified and represented in the wavelet domain. By using special variants of the compressed format, efficient implementations of essential image processing algorithms are possible and demonstrate the potential of the approach. From the technical perspective, the GPU-based framework "Cascada" has been developed in the course of this thesis. The introduction of object-oriented concepts to shader programming, as well as a hierarchical representation of computation and/or visualization procedures led to a simplified utilization of graphics hardware while maintaining competitive performance. This is shown with different implementations throughout the contributions, as well as two clinical projects in the field of diagnosis assistance. On the one hand the semi-automatic segmentation of low-resolution MRI data sets of the human liver is evaluated. On the other hand different possibilities in assessing abdominal aortic aneurysms are discussed; both projects make use of graphics hardware. In addition, "Cascada" provides extensions towards recent general-purpose programming architectures and a modular design for future developments.
In this work has been examined, how the existing model of the simulation of cables and hoses can be advanced. Therefore an investigation has been made on the main influences to the shape simulation and the factors of constraints and side conditions were analyzed. For the validation of the accuracy, the simulation has to be compared to real specimen behavior. To obtain a very precise digitalization of the shape, the choice was made to use a laser scanner that converts the pointcloud into a .vrml file which can be imported into the simulation environment. The assumption was that the simulation method itself has the highest impact to the simulated shape. This is why the capabilities of the most sophisticated methods have been analyzed. The main criterion for the success of a simulation approach proved not to be accuracy, as expected. Process integration and usability showed to be of higher interest for the efficient exertion. Other factors like the pricing, the functionality and the real-time capability were assayed as well. The analyzed methods are based on the solution of the equations of elasticity with different ways of discetization, finite-elements and a spring-impulse-system. Since the finite-element-system takes several minutes for the computation of the shape and the spring-impulse-system reacts retarded on user manipulation, the competitiveness of these approaches is low. The other methods distinguish more in real-time performance, data interfaces and functionality than in accuracy. For the accuracy of a system, the consideration of other factors proved to be very important. As one of these main factors, the accurate assignment of the material properties was indicated. Until the start of this work, only the finite-element-approach dealt with this factor, but no documentation or validation is provided. In the publications of the other methods, the material properties are estimated to obtain a plausible simulation shape. Therefore the specific material values of real specimen have been measured and assigned to the simulation. With the comparison to the real shape it has been proven that the accuracy is very high with the measured properties. Since these measurements are very costly and time consuming, an investigation on a faster and cheaper way to obtain these values has been made. It has been assumed that with the knowledge of the cross-section it should be possible to compute the specimen behavior. Since the braid distribution changes individually from specimen to specimen, a more general way to obtain the values needed to be found. The program composer has been developed, where only the number of the different braids and the taping is entered. It computes with very high precision the stiffness, the density and the final diameter of the bundle. With the measured values and the fitting to the real shape it has been proven that the simulation approach reflects the precise behavior of cables and hoses. Since the stiffness of the single braids is wasteful to measure, a measurement setup was created where the stiffness has a large impact to the shape. With known density, the stiffness of the specimen can be reconstructed precisely. Thus a fast and beneficial way of obtaining the stiffness of a cable has been invented. The poissons ratio of cables and bundles cannot be measured with a tensile test, since the inner structure is very complex. For hoses, the variation of the inner diameter has been measured during the tensile test as well. The resulting values were reasonable, but their accuracy could not be proven. For cables and hoses, it has been tried to obtain the poissons ratio via the computation of the cross section, but the influence of individual changes and the crosstalk of the braids is very high. Therefore a setup was constructed where the torsion stiffness can be measured. For cables and hoses, the individual cross-sections and taping lead to varying results. For hoses, expected and repeatable good values for the poissons ratio were obtained. The low influence of the poisons ratio in the range between 0 and 0.5 has been proven. Therefore we decided to follow the advice of [Old06] and our own experiences to set the poisons ratio for cables and bundles to 0.25. With the knowledge of the measurability and the capabilities of the developed program composer, a procedure to obtain material properties for bundles has been designed. 1. Measurement of the braid density with via pyknometer or mass, length and diameter. 2. Empirical reconstruction of the stiffness with the designed setup. 3. Composing the bundle with the program composer. 4. Adding a factor for the taping and transfer the values to the simulation. The model of the cable simulation has been improved as follows: The main influences in the simulation of cables and hoses are the simulation method, the material properties and the geometric constraints. To obtain higher accuracy, an investigation on the correct material properties is indispensable. The scientific determination of material properties for the simulation of cables, bundles and hoses has been performed for the first time. The influence of geometrical constraints has been analyzed and documented. The next steps are the analysis of pre-deformation and further investigations to the determination of the poisons ratio with a more precise torsion test. All analysis were made with the simulation approach fleXengine. A comparison to other simulation methods would be of high interest.
This work is about three subjects: Virtualisation, real-time computing and parallel computing. Taken by itself, each of these subjects has already been wellresearched, however, when considering all three together, as is necessary when looking at embedded systems, numerous questions as well as new possibilities arise. In this work we develop models describing the behaviour and requirements of real-time applications which execute in a hierarchy of processes as they do when running in a virtual machine. Also, the real-time capabilities of existing virtual machines are evaluated and new interfaces for virtualisation of multiprocessor machines which take into account the characteristics of embedded systems"specifically real-time computing" are defined, implemented and tested. This enables safe, secure and efficient coexistence of programs with largely differing time constraints within separate virtual machines on a single, common multiprocessor computer.
This dissertation introduces a methodology for formal specification and verification of user interfaces under security aspects. The methodology allows to use formal methods pervasively in the specification and verification of human-computer interaction. This work consists of three parts. In the first part, a formal methodology for the description of human-computer interaction is developed. In the second part, existing definitions of computer security are adapted for human-computer interaction and formalized. A generic formal model of human-computer interaction is developed. In the third part, the methodology is applied to the specification and verification of a secure email client.
Probability propagation nets
(2008)
This work introduces a Petri net representation for the propagation of probabilities and likelihoods, which can be applied to probabilistic Horn abduction, fault trees, and Bayesian networks. These so-called "probability propagation nets" increase the transparency of propagation processes by integrating structural and dynamical aspects into one homogeneous representation. It is shown by means of popular examples that probability propagation nets improve the understanding of propagation processes - especially with respect to the Bayesian propagation algorithms - and thus are well suited for the analysis and diagnosis of probabilistic models. Representing fault trees with probability propagation nets transfers these possibilities to the modeling of technical systems.
In the last years the e-government concentrated on the administrative aspects of administrative modernisation. In the next step the e-discourses will gain in importance as an instrument of the public-friendliness and means of the e-democracy/e-participation. With growing acceptance of such e-discourses, these will fastly reach a complexity, which could not be mastered no more by the participants. Many impressions, which could be won from presence discussions, will be lacking now. Therefore the exposed thesis has the objective of the conception and the prototypical implementation of an instrument (discourse meter), by which the participants, in particular the moderators of the e-discourse, are capable to overlook the e-discourse at any time and by means of it, attain their discourse awareness. Discourse awareness of the present informs about the current action in the e-discourse and discourse awareness of the past about the past action, by which any trends become visible. The focus of the discourse awareness is located in the quantitative view of the action in the e-discourse. From the model of e-discourse, which is developed in this thesis, the questions of discourse awareness are resulting, whose concretion is the basis for the implementation of the discourse meter. The discourse sensors attached to the model of the e-discourse are recording the actions of the e-discourse, showing events of discourse, which are represented by the discourse meter in various forms of visualizations. The concept of discourse meter offers the possibility of discourse awareness relating to the present as monitoring and the discourse awareness relating to the past as query (quantitative analysis) to the moderators of the e-discourse.