@phdthesis{Hanning2002, author = {Hanning, Tobias}, title = {Vektorielle Mehrniveaupassung. Anwendungen in der Bildsegmentierung}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-295}, school = {Universit{\"a}t Passau}, year = {2002}, abstract = {Die Anwendungen der vektoriellen Mehrniveaupassung in der Bildsegmentierung stehen in unmittelbarer Nachbarschaft zum verbreiteten Ansatz, Bilder mit Methoden der Variationsrechnung {\"u}ber einen Energieterm zu segmentieren. Beiden Verfahren ist gemeinsam, daß sie versuchen, das gegebene Bild durch st{\"u}ckweise stetige Funktionen zu approximieren. Die maximalen Teilmengen des Definitionsbereichs, auf denen die approximierende Funktion stetig ist, bilden dann die Segmente. Im Gegensatz zu dem in der Literatur h{\"a}ufig unter dem Schlagwort Mumford-Shah-Modell bekannten Energieminimierungsverfahren ist der Raum der Funktionen, mit denen das Bild approximiert wird, bei der vektoriellen Mehrniveaupassung ein endlicher Vektorraum. Ein weiterer Unterschied zu diesem Ansatz ist das System der erlaubten Mengen. Es werden nur Segmentierungen erlaubt, deren Segmente aus diesem Mengensystem sind. Die durch diese Einschr{\"a}nkung schlankere Theorie f{\"u}hrt zu einer gesicherten Existenz einer optimalen L{\"o}sung des Segmentierungsproblems, die der g{\"a}ngigen Vorstellung einer Segmentierung gen{\"u}gt. Die Berechnung lokaler Optima ist algorithmisch innerhalb der Theorie umsetzbar.}, subject = {Bildsegmentierung}, language = {de} } @phdthesis{Kunze2011, author = {Kunze, Kai}, title = {Compensating for On-Body Placement Effects in Activity Recognition}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-26114}, school = {Universit{\"a}t Passau}, year = {2011}, abstract = {This thesis investigates, how placement variations of electronic devices influence the possibility of using sensors integrated in those devices for context recognition. The vast majority of context recognition research assumes well defined, fixed sen- sor locations. Although this might be acceptable for some application domains (e.g. in an industrial setting), users, in general, will have a hard time coping with these limitations. If one needs to remember to carry dedicated sensors and to adjust their orientation from time to time, the activity recognition system is more distracting than helpful. How can we deal with device location and orientation changes to make context sensing mainstream? This thesis presents a systematic evaluation of device placement effects in context recognition. We first deal with detecting if a device is carried on the body or placed somewhere in the environ- ment. If the device is placed on the body, it is useful to know on which body part. We also address how to deal with sensors changing their position and their orientation during use. For each of these topics some highlights are given in the following. Regarding environmental placement, we introduce an active sampling ap- proach to infer symbolic object location. This approach requires only simple sensors (acceleration, sound) and no infrastructure setup. The method works for specific placements such as "on the couch", "in the desk drawer" as well as for general location classes, such as "closed wood compartment" or "open iron sur- face". In the experimental evaluation we reach a recognition accuracy of 90\% and above over a total of over 1200 measurements from 35 specific locations (taken from 3 different rooms) and 12 abstract location classes. To derive the coarse device placement on the body, we present a method solely based on rotation and acceleration signals from the device. It works independent of the device orientation. The on-body placement recognition rate is around 80\% over 4 min. of unconstrained motion data for the worst scenario and up to 90\% over a 2 min. interval for the best scenario. We use over 30 hours of motion data for the analysis. Two special issues of device placement are orientation and displacement. This thesis proposes a set of heuristics that significantly increase the robustness of motion sensor-based activity recognition with respect to sen- sor displacement. We show how, within certain limits and with modest quality degradation, motion sensor-based activity recognition can be implemented in a displacement tolerant way. We evaluate our heuristics first on a set of synthetic lower arm motions which are well suited to illustrate the strengths and limits of our approach, then on an extended modes of locomotion problem (sensors on the upper leg) and finally on a set of exercises performed on various gym machines (sensors placed on the lower arm). In this example our heuristic raises the dis- placed recognition rate from 24\% for a displaced accelerometer, which had 96\% recognition when not displaced, to 82\%.}, subject = {Kontextbezogenes System}, language = {en} } @phdthesis{Guppenberger2010, author = {Guppenberger, Michael}, title = {Enhancing Information Systems with Event-Handling - A Non-Invasive Approach}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-22485}, school = {Universit{\"a}t Passau}, year = {2010}, abstract = {Due to the immense advance of widely accessible information systems in industrial applications, science, education and every day use, it becomes more and more difficult for users of those information systems to keep track with new and updated information. An approach to cope with this problem is to go beyond traditional search facilities and instead use the users' profiles to monitor data changes and to actively inform them about these updates - an aspect that has to be explicitly developed and integrated into a variety of information systems. This is traditionally done in an individual way, depending on the application and its platform. In this dissertation, we present a novel approach to model the semantic interrelations that specify which users to inform about which updates, based on the underlying model of the respective information system. For the first time, a meta-model that allows information system designers to tag an arbitrary data model and thus specify the event-handling semantics is presented. A formal specification of how to interpret meta-models to determine the receivers of the events completes the presented concept. For the practical realization of this new concept, model driven architecture (MDA) shows to be an ideal technical means. Using our newly developed UML profile based on data-modelling standards, an implementation of the event-handling specification can automatically be generated for a variety of different target platforms, like e.g. relational databases, using triggers. This meta-approach makes the proposed solution ideal with respect to maintainability and genericity. Our solution significantly reduces the overall development efforts for an event-handling facility. In addition, the enhanced model of the information system can be used to generate an implementation that also fulfils non-functional requirements like high performance and extensibility. The overall framework, consisting of the domain specific language (i.e. the meta-model), formal and technical transformations of how to interpret the enhanced information system model and a cost-based optimizing strategy, constitutes an integrated approach, offering several advantages over traditional implementation techniques: our framework can be applied to new information systems as well as to legacy applications without having to modify existing systems; it offers an extensible, easy-to-use, generic and thus re-usable solution and it can be tailored to and optimized for many use cases, as the practical evaluation presented in this dissertation verifies.}, subject = {Notifikation}, language = {en} } @phdthesis{Berl2011, author = {Berl, Andreas}, title = {Energy Efficiency in Office Computing Environments}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-22516}, school = {Universit{\"a}t Passau}, year = {2011}, abstract = {The increasing cost of energy and the worldwide desire to reduce CO2 emissions has raised concern about the energy efficiency of information and communication technology. Whilst research has focused on data centres recently, this thesis identifies office computing environments as significant consumers of energy. Office computing environments offer great potential for energy savings: On one hand, such environments consist of a large number of hosts. On the other hand, these hosts often remain turned on 24~hours per day while being underutilised or even idle. This thesis analyzes the energy consumption within office computing environments and suggests an energy-efficient virtualized office environment. The office environment is virtualized to achieve flexible virtualized office resources that enable an energy-based resource management. This resource management stops idle services and idle hosts from consuming resources within the office and consolidates utilised office services on office hosts. This increases the utilisation of some hosts while other hosts are turned off to save energy. The suggested architecture is based on a decentralized approach that can be applied to all kinds of office computing environments, even if no centralized data centre infrastructure is available. The thesis develops the architecture of the virtualized office environment together with an energy consumption model that is able to estimate the energy consumption of hosts and network within office environments. The model enables the energy-related comparison of ordinary and virtualized office environments, considering the energy-efficient management of services. Furthermore, this thesis evaluates energy efficiency and overhead of the suggested approach. First, it theoretically proves the energy efficiency of the virtualized office environment with respect to the energy consumption model. Second, it uses Markov processes to evaluate the impact of user behaviour on the suggested architecture. Finally, the thesis develops a discrete-event simulation that enables the simulation and evaluation of office computing environments with respect to varying virtualization approaches, resource management parameters, user behaviour, and office equipment. The evaluation shows that the virtualized office environment saves more than half of the energy consumption within office computing environments, depending on user behaviour and office equipment.}, subject = {Energieeffizienz}, language = {en} } @phdthesis{Hoelbling2011, author = {H{\"o}lbling, G{\"u}nther}, title = {Personalized Means of Interacting with Multimedia Content}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-24210}, school = {Universit{\"a}t Passau}, year = {2011}, abstract = {Today the world of multimedia is almost completely device- and content-centered. It focuses it's energy nearly exclusively on technical issues such as computing power, network specifics or content and device characteristics and capabilities. In most multimedia systems, the presentation of multimedia content and the basic controls for playback are main issues. Because of this, a very passive user experience, comparable to that of traditional TV, is most often provided. In the face of recent developments and changes in the realm of multimedia and mass media, this "traditional" focus seems outdated. The increasing use of multimedia content on mobile devices, along with the continuous growth in the amount and variety of content available, make necessary an urgent re-orientation of this domain. In order to highlight the depth of the increasingly difficult situation faced by users of such systems, it is only logical that these individuals be brought to the center of attention. In this thesis we consider these trends and developments by applying concepts and mechanisms to multimedia systems that were first introduced in the domain of usercentrism. Central to the concept of user-centrism is that devices should provide users with an easy way to access services and applications. Thus, the current challenge is to combine mobility, additional services and easy access in a single and user-centric approach. This thesis presents a framework for introducing and supporting several of the key concepts of user-centrism in multimedia systems. Additionally, a new definition of a user-centric multimedia framework has been developed and implemented. To satisfy the user's need for mobility and flexibility, our framework makes possible seamless media and service consumption. The main aim of session mobility is to help people cope with the increasing number of different devices in use. Using a mobile agent system, multimedia sessions can be transferred between different devices in a context-sensitive way. The use of the international standard MPEG-21 guarantees extensibility and the integration of content adaptation mechanisms. Furthermore, a concept is presented that will allow for individualized and personalized selection and face the need for finding appropriate content. All of which can be done, using this approach, in an easy and intuitive way. Especially in the realm of television, the demand that such systems cater to the need of the audience is constantly growing. Our approach combines content-filtering methods, state-of-the-art classification techniques and mechanisms well known from the area of information retrieval and text mining. These are all utilized for the generation of recommendations in a promising new way. Additionally, concepts from the area of collaborative tagging systems are also used. An extensive experimental evaluation resulted in several interesting findings and proves the applicability of our approach. In contrast to the "lean-back" experience of traditional media consumption, interactive media services offer a solution to make possible the active participation of the audience. Thus, we present a concept which enables the use of interactive media services on mobile devices in a personalized way. Finally, a use case for enriching TV with additional content and services demonstrates the feasibility of this concept.}, subject = {Empfehlungssystem}, language = {en} } @phdthesis{Johns2009, author = {Johns, Martin}, title = {Code Injection Vulnerabilities in Web Applications - Exemplified at Cross-site Scripting}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-23626}, school = {Universit{\"a}t Passau}, year = {2009}, abstract = {The majority of all security problems in today's Web applications is caused by string-based code injection, with Cross-site Scripting (XSS)being the dominant representative of this vulnerability class. This thesis discusses XSS and suggests defense mechanisms. We do so in three stages: First, we conduct a thorough analysis of JavaScript's capabilities and explain how these capabilities are utilized in XSS attacks. We subsequently design a systematic, hierarchical classification of XSS payloads. In addition, we present a comprehensive survey of publicly documented XSS payloads which is structured according to our proposed classification scheme. Secondly, we explore defensive mechanisms which dynamically prevent the execution of some payload types without eliminating the actual vulnerability. More specifically, we discuss the design and implementation of countermeasures against the XSS payloads Session Hijacking'', Cross-site Request Forgery'', and attacks that target intranet resources. We build upon this and introduce a general methodology for developing such countermeasures: We determine a necessary set of basic capabilities an adversary needs for successfully executing an attack through an analysis of the targeted payload type. The resulting countermeasure relies on revoking one of these capabilities, which in turn renders the payload infeasible. Finally, we present two language-based approaches that prevent XSS and related vulnerabilities: We identify the implicit mixing of data and code during string-based syntax assembly as the root cause of string-based code injection attacks. Consequently, we explore data/code separation in web applications. For this purpose, we propose a novel methodology for token-level data/code partitioning of a computer language's syntactical elements. This forms the basis for our two distinct techniques: For one, we present an approach to detect data/code confusion on run-time and demonstrate how this can be used for attack prevention. Furthermore, we show how vulnerabilities can be avoided through altering the underlying programming language. We introduce a dedicated datatype for syntax assembly instead of using string datatypes themselves for this purpose. We develop a formal, type-theoretical model of the proposed datatype and proof that it provides reliable separation between data and code hence, preventing code injection vulnerabilities. We verify our approach's applicability utilizing a practical implementation for the J2EE application server.}, subject = {Computersicherheit}, language = {en} } @phdthesis{Rabl2011, author = {Rabl, Tilmann}, title = {Efficiency in Cluster Database Systems - Dynamic and Workload-Aware Scaling and Allocation}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-25821}, school = {Universit{\"a}t Passau}, year = {2011}, abstract = {Database systems have been vital in all forms of data processing for a long time. In recent years, the amount of processed data has been growing dramatically, even in small projects. Nevertheless, database management systems tend to be static in terms of size and performance which makes scaling a difficult and expensive task. Because of performance and especially cost advantages more and more installed systems have a shared nothing cluster architecture. Due to the massive parallelism of the hardware programming paradigms from high performance computing are translated into data processing. Database research struggles to keep up with this trend. A key feature of traditional database systems is to provide transparent access to the stored data. This introduces data dependencies and increases system complexity and inter process communication. Therefore, many developers are exchanging this feature for a better scalability. However, explicitly managing the data distribution and data flow requires a deep understanding of the distributed system and reduces the possibilities for automatic and autonomic optimization. In this thesis we present an approach for database system scaling and allocation that features good scalability although it keeps the data distribution transparent. The first part of this thesis analyzes the challenges and opportunities for self-scaling database management systems in cluster environments. Scalability is a major concern of Internet based applications. Access peaks that overload the application are a financial risk. Therefore, systems are usually configured to be able to process peaks at any given moment. As a result, server systems often have a very low utilization. In distributed systems the efficiency can be increased by adapting the number of nodes to the current workload. We propose a processing model and an architecture that allows efficient self-scaling of cluster database systems. In the second part we consider different allocation approaches. To increase the efficiency we present a workload-aware, query-centric model. The approach is formalized; optimal and heuristic algorithms are presented. The algorithms optimize the data distribution for local query execution and balance the workload according to the query history. We present different query classification schemes for different forms of partitioning. The approach is evaluated for OLTP and OLAP style workloads. It is shown that variants of the approach scale well for both fields of application. The third part of the thesis considers benchmarks for large, adaptive systems. First, we present a data generator for cloud-sized applications. Due to its architecture the data generator can easily be extended and configured. A key feature is the high degree of parallelism that makes linear speedup for arbitrary numbers of nodes possible. To simulate systems with user interaction, we have analyzed a productive online e-learning management system. Based on our findings, we present a model for workload generation that considers the temporal dependency of user interaction.}, subject = {Verteiltes Datenbanksystem}, language = {en} } @phdthesis{Houyou2009, author = {Houyou, Amine Mohamed}, title = {Context-Aware Mobility: A Distributed Approach to Context Management}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-17975}, school = {Universit{\"a}t Passau}, year = {2009}, abstract = {The recent development of a whole plethora of new wireless technologies, such as IEEE 802.11, IEEE 802.15, IEEE 802.16, UMTS, and more recently LTE, etc, has triggered several efforts to integrate these technologies in a converged world of transparent and ubiquitous wireless connectivity. Most of these technologies have evolved around a certain use case and with some user behaviour being assumed; however, there still lacks a holistic solution to adapt access to user needs, in an automatic and transparent manner. One major problem that has to be addressed first, is mobility management between heterogeneous wireless networks. Current mobility management solutions mostly originate from cellular networking systems, which are operator specific, centralised, and focused on a single link technology. In order to deal with the wireless diversity of future wireless and mobile Internet, a new approach is needed. Adaptive wireless connectivity that is tailored around the user needs and capabilities is named context-aware mobility management. Context refers to the information describing the surroundings of the user as well as his/her behaviour, and additional semantic information that could optimise the adaption process. Context management normally entails discovering and tracking context, reasoning based on the discovered information, then adapting (or acting) upon the context-aware application or system. This context management chain is adapted throughout the thesis to the task of context-aware mobility management. The added complexity is necessary to adapt the ubiquitous access to the condition of both the user and the surrounding networks, while assuming that overlapping wireless networks could still be managed in separate management domains. Linking these management domains and aggregating this composite information in the form of a network context is one of the major contributions of this work. An overlay-based solution takes into account this scattered nature of the context management system, which is modelled as a decentralised dynamic location-based service. The proposed architecture is generalised to support ubiquitous location-based services, and a design methodology is proposed to ensure the localised impact of mobility-led context retrieval overhead.}, subject = {Netze}, language = {en} } @phdthesis{Ogris2009, author = {Ogris, Georg}, title = {Multi-modal on-body sensing of human activities}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-17930}, school = {Universit{\"a}t Passau}, year = {2009}, abstract = {Increased usage and integration of state-of-the-art information technology in our everyday work life aims at increasing the working efficiency. Due to unhandy human-computer-interaction methods this progress does not always result in increased efficiency, for mobile workers in particular. Activity recognition based contextual computing attempts to balance this interaction deficiency. This work investigates wearable, on-body sensing techniques on their applicability in the field of human activity recognition. More precisely we are interested in the spotting and recognition of so-called manipulative hand gestures. In particular the thesis focuses on the question whether the widely used motion sensing based approach can be enhanced through additional information sources. The set of gestures a person usually performs on a specific place is limited -- in the contemplated production and maintenance scenarios in particular. As a consequence this thesis investigates whether the knowledge about the user's hand location provides essential hints for the activity recognition process. In addition, manipulative hand gestures -- due to their object manipulating character -- typically start in the moment the user's hand reaches a specific place, e.g. a specific part of a machinery. And the gestures most likely stop in the moment the hand leaves the position again. Hence this thesis investigates whether hand location can help solving the spotting problem. Moreover, as user-independence is still a major challenge in activity recognition, this thesis investigates location context as a possible key component in a user-independent recognition system. We test a Kalman filter based method to blend absolute position readings with orientation readings based on inertial measurements. A filter structure is suggested which allows up-sampling of slow absolute position readings, and thus introduces higher dynamics to the position estimations. In such a way the position measurement series is made aware of wrist motions in addition to the wrist position. We suggest location based gesture spotting and recognition approaches. Various methods to model the location classes used in the spotting and recognition stages as well as different location distance measures are suggested and evaluated. In addition a rather novel sensing approach in the field of human activity recognition is studied. This aims at compensating drawbacks of the mere motion sensing based approach. To this end we develop a wearable hardware architecture for lower arm muscular activity measurements. The sensing hardware based on force sensing resistors is designed to have a high dynamic range. In contrast to preliminary attempts the proposed new design makes hardware calibration unnecessary. Finally we suggest a modular and multi-modal recognition system; modular with respect to sensors, algorithms, and gesture classes. This means that adding or removing a sensor modality or an additional algorithm has little impact on the rest of the recognition system. Sensors and algorithms used for spotting and recognition can be selected and fine-tuned separately for each single activity. New activities can be added without impact on the recognition rates of the other activities.}, subject = {Kontextbezogenes System}, language = {de} } @phdthesis{Brunner2010, author = {Brunner, Wolfgang}, title = {Cyclic Level Drawings of Directed Graphs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-17962}, school = {Universit{\"a}t Passau}, year = {2010}, abstract = {The Sugiyama framework proposed in the seminal paper of 1981 is one of the most important algorithms in graph drawing and is widely used for visualizing directed graphs. In its common version, it draws graphs hierarchically and, hence, maps the topological direction to a geometric direction. However, such a hierarchical layout is not possible if the graph contains cycles, which have to be destroyed in a preceding step. In certain application and problem settings, e.g., bio sciences or periodic scheduling problems, it is important that the cyclic structure of the input graph is preserved and clearly visible in drawings. Sugiyama et al. also suggested apart from the nowadays standard horizontal algorithm a cyclic version they called recurrent hierarchies. However, this cyclic drawing style has not received much attention since. In this thesis we consider such cyclic drawings and investigate the Sugiyama framework for this new scenario. As our goal is to visualize cycles directly, the first phase of the Sugiyama framework, which is concerned with removing such cycles, can be neglected. The cyclic structure of the graph leads to new problems in the remaining phases, however, for which solutions are proposed in this thesis. The aim is a complete adaption of the Sugiyama framework for cyclic drawings. To complement our adaption of the Sugiyama framework, we also treat the problem of cyclic level planarity and present a linear time cyclic level planarity testing and embedding algorithm for strongly connected graphs.}, subject = {Graphenzeichnen}, language = {en} }