05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Integration von Data Mining und Online Analytical Processing : eine Analyse von Datenschemata, Systemarchitekturen und Optimierungsstrategien(2003) Schwarz, Holger; Mitschang, Bernhard (Prof. Dr.-Ing. habil.)Die technischen Möglichkeiten, Daten zu erfassen und dauerhaft zu speichern, sind heute so ausgereift, dass insbesondere in Unternehmen und anderen Organisationen große Datenbestände verfügbar sind. In diesen Datenbeständen, häufig als Data Warehouse bezeichnet, sind alle relevanten Informationen zu den Organisationen selbst, den in ihnen ablaufenden Prozessen sowie deren Interaktion mit anderen Organisationen enthalten. Vielfach stellt die zielgerichtete Analyse der Datenbestände den entscheidenden Erfolgsfaktor für Organisationen dar. Zur Analyse der Daten in einem Data Warehouse sind verschiedenste Ansätze verfügbar und erprobt. Zwei der wichtigsten Vertreter sind das Online Analytical Processing (OLAP) und das Data Mining. Beide setzen unterschiedliche Schwerpunkte und werden bisher in der Regel weitgehend isoliert eingesetzt. In dieser Arbeit wird zunächst gezeigt, dass eine umfassende Analyse der Datenbestände in einem Data Warehouse nur durch den integrierten Einsatz beider Analyseansätze erzielt werden kann. Einzelne Fragestellungen, die sich aus diesem Integrationsbedarf ergeben werden ausführlich diskutiert. Zu den betrachteten Fragestellungen gehört die geeignete Modellierung der Daten in einem Data Warehouse. Bei der Bewertung gängiger Modellierungsansätze fließen insbesondere die Anforderungen ein, die sich durch den beschriebenen Integrationsansatz ergeben. Als Ergebnis wird ein konzeptuelles Datenmodell vorgestellt, das Informationen in einer Weise strukturiert, die für OLAP und Data Mining gleichermaßen geeignet ist. Im Bereich der logischen Modellierung werden schließlich diejenigen Schematypen identifiziert, die die Integration der Analyseansätze geeignet unterstützen. Im nächsten Schritt sind die für Data Mining und OLAP unterschiedlichen Systemarchitekturen Gegenstand dieser Arbeit. Deren umfassende Diskussion ergibt eine Reihe von Defiziten. Dies führt schließlich zu einer erweiterten Systemarchitektur, die die Schwachstellen beseitigt und die angestrebte Integration geeignet unterstützt. Die erweiterte Systemarchitektur weist eine Komponente zur anwendungsunabhängigen Optimierung unterschiedlicher Analyseanwendungen auf. Ein dritter Schwerpunkt dieser Arbeit besteht in der Identifikation geeigneter Optimierungsansätze hierfür. Die Bewertung der Ansätze wird einerseits qualitativ durchgeführt. Andererseits wird das Optimierungspotenzial der einzelnen Ansätze auch auf der Grundlage umfangreicher Messreihen gezeigt.Item Open Access Scalable computer network emulation using node virtualization and resource monitoring(2011) Maier, Steffen Dirk; Rothermel, Kurt (Prof. Dr. rer. nat. Dr. h. c.)Ongoing development of computer network technology requires new communication protocols on all layers of the protocol stack to adapt to and to exploit technology specifics. The performance of new protocol implementations has to be evaluated before deployment. Computer network emulation enables the execution of real unmodified protocol implementations within a configurable synthetic environment. Since network properties are reproduced synthetically, emulation supports reproducible measurement results for wired and wireless networks. Meaningful evaluation scenarios typically involve a large number of communicating nodes. Reproducing the network properties of the medium access control layer can be accomplished efficiently on cheap common off the shelf computers and allows to evaluate network protocols, transport protocols, and applications. However, meaningful emulation scenario sizes often require more nodes than affordable computers. To scale the number of nodes in an emulation scenario beyond the available computers, we discuss approaches to virtualization and operating system partitioning. Focusing on the latter, we argue for virtual protocol stacks, which provide an extremely lightweight node virtualization enabling the execution of multiple instances of software to be evaluated on each physical computer. To connect virtual nodes on the same and on different computers, we design and implement a highly efficient software communication switch. A centralized emulation control component distributes dynamic network property updates which result from node mobility for instance. To handle the large number of nodes and thus increased updates, we propose a hierarchical control where the central component delegates updates to sub-components distributed over the computers of an emulation system. Extensive evaluations show the scalability of our virtualized network emulation system. Virtual nodes executed on the same computer share its limited resources. Hosting too many virtual nodes on the same computer may lead to resource contention. This can cause unrealistic measurement results and is thus undesirable. Discussing different approaches to handle resource contention, we argue for detection and recovery. We define quality criteria that allow the detection of resource contention. In order to observe those quality criteria during emulation experiments, we propose a highly lightweight monitoring approach. Our monitoring is based on instrumenting an operating system kernel and observing basic resource scheduling events. This enables the detection of even peak resource usage within a split second. Thorough evaluations demonstrate the effectiveness of quality criteria and monitoring as well as the negligible overhead of our monitoring approach.Item Open Access Investigating dynamics by multilevel phase space discretization(2006) Fundinger, Danny Georg; Levi, Paul (Prof. Dr.)The subject of the thesis is the numerical investigation of dynamical systems. The aim is to provide approaches for the localization of several topological structures which are of vital importance for the global analysis of dynamical systems, namely, periodic orbits, the chain recurrent set, repellers, attractors and their domains of attraction as well as stable, unstable and connecting manifolds. The techniques introduced do not require any a priori knowledge about a system, and are also not restricted by the stability of the solution. Furthermore, they can generally be applied to a wide range of dynamical systems. Two theoretical concepts are considered to be at the center of the research - symbolic analysis and the RIM method. The underlying basic approach for both of them is multilevel phase space discretization. This means that a part of the phase space, the area of investigation, is subdivided in a finite number of sets. Then, instead of each point of the phase space, only these sets are subject of further analysis. The main target of every method proposed is to find those sets which contain parts of the solution and subdivide them into smaller parts until a desired accuracy is reached. In case of symbolic analysis, a directed graph is constructed which represents the structure of the state space for the investigated dynamical system. This graph is called the symbolic image of the focused system and can be seen as an approximation of the system flow. The theoretical background regarding the symbolic image graph as well as the constructive methods applied on it were already described in a series of works by G. Osipenko. In this work, strategies are introduced for a practical application. This requires the extension of the theoretical concepts and the development of appropriate algorithms and data structures. In practice, it turned out that these aspects are essential cornerstones for the usability of the discussed methods. Also some sophisticated tunings of the basic methods are proposed in order to extent the field of practical investigation. Although symbolic analysis can be seen as the main stimulation of this work, the investigation was not limited to it. Indeed, several shortcomings regarding the solution of some problems can be observed if the method is applied in practice. This led to the development of the RIM method. The core intention of the method is to solve the root finding problem. The standard approach toward this task is the application of an iteration scheme based on the Newton method. However, it has shown that such Newton schemes have several structural disadvantages which are especially crucial in the context of the fields of investigation which are relevant to this work. The RIM method proposes an alternative approach which does not require the application of any Newton-like method. Numerical case studies revealed that in several nontrivial scenarios the RIM method provides better results than both, symbolic analysis as well as Newton-based methods. Two applications of the RIM method for the investigation of dynamical systems are provided. One of them is the detection of periodic points. The other is the computation of stable manifolds. The proposed methods contribute not only to the direct investigation and simulation of specific dynamical processes but also to the research in the field of dynamical system theory in general. This is due to the fact that progress in theory depends to a large extent on the observation and investigation of phenomenons. These phenomenons can often only be revealed, analyzed and verified by numerical experiments. The presented numerical case studies give some concrete examples for the application of the methods. Hereby, the dynamical models are taken from different fields of scientific research, like geography, biology, meteorology, or physics.Item Open Access Effiziente Gestaltung und Anwendung von attributbasierter Zugriffskontrolle für RESTful Services(2019) Hüffmeyer, Marc; Mitschang, Bernhard (Prof. Dr.)Item Open Access Interaktion und Koordination in Multiagentensystemen(2001) Muscholl, Klaus Matthias; Levi, Paul (Prof. Dr.)Das Zusichern von kohärentem Verhalten in Multiagentensystemen ist durch die inhärente Verteiltheit des Systems, als auch durch den unabhängigen Entwurf der Agenten bei offenen Systemen, ein weithin ungelöstes Problem. In der vorliegenden Dissertation wird ein entwurfstechnischer Ansatz vorgestellt, welcher mit Hilfe von Interaktionsverfahren Kohärenz sicherstellt. Interaktionsverfahren werden dabei durch das Interaktionsmodell beschrieben. Die Grundidee besteht darin, daß Agenten durch die Teilnahme an einer Interaktion einen Teil ihrer Autonomie an das die Interaktion beschreibende Verfahren und seine Entscheidungsmechanismen abtreten und sich ihm unterordnen. Dies wird dadurch erzielt, daß ein Interaktionsverfahren die Koordination der an ihn übertragenen Kompetenzen übernimmt. Ein Interaktionsverfahren ist somit gegenüber den teilnehmenden Agenten weisungsbefugt. Um an Interaktionsverfahren teilnehmen zu können, muß ein Agent eine Schnittstelle unterstützen, welche es dem Interaktionsverfahren ermöglicht, auf die an ihn übertragen Kompetenz zuzugreifen und die kollektiv getroffenen Entscheidungen im einzelnen durchzusetzen. Hierzu sind unabhängig von Interaktionsverfahren für einen Anwendungsbereich Dienstklassen definiert, welche Schnittstellen zu Fähigkeiten eines Agenten bilden. Ein Interaktionsverfahren definiert das Ablaufschema einer Interaktion. Das Ablaufschema abstrahiert von Agenten in Form von Rollen. Das Schema ist in einzelne Phasen strukturiert und definiert, wie die Rollen untereinander interagieren. Rollen sind die kleinsten aktiven Einheiten des Interaktionsmodells und nur innerhalb einer Phase gültig. Agenten, welche an einem Interaktionsverfahren teilnehmen, werden durch Rollen gesteuert, die ihnen in den jeweiligen Phasen zugewiesen werden. Die vorliegende Arbeit ist Bestandteil des Architekturkonzepts von Robotersystemen im Comros-Projekt.Item Open Access Optimierung datenintensiver Workflows: Konzepte und Realisierung eines heuristischen, regelbasierten Optimierers(2011) Vrhovnik, Marko; Mitschang, Bernhard (Prof. Dr.-Ing. habil.)Um die Modellierung datenintensiver Workflows, die große relationale Datenmengen verarbeiten, zu vereinfachen, wurden Workflowbeschreibungssprachen, wie BPEL, von führenden Herstellern von Workflow- und Datenbankmanagementsystemen um SQL-Funktionalität erweitert. Dadurch müssen Datenverarbeitungsoperationen, wie SQL-Anweisungen oder Aufrufe benutzerdefinierter Prozeduren, nicht mehr in Web-Services gekapselt werden, sondern können direkt auf der Workflowebene definiert werden. Daraus resultiert eine neue Möglichkeit der Anfrageoptimierung, die existierende Optimierungsansätze in Datenbanksystemen ergänzt: Suboptimal modellierte Datenverarbeitungsoperationen lassen sich in einer Workflowbeschreibung unter Verwendung von Restrukturierungsregeln derart transformieren, dass sie von einem Workflow- bzw. Datenbankmanagementsystem wesentlich effizienter ausgeführt werden können. In dieser Doktorarbeit werden Konzepte zur Realisierung eines heuristischen, regelbasierten Optimierers für datenintensive Workflows vorgestellt. Der Optimierer wendet eine Regelbasis gemäß einer wohldefinierten Kontrollstrategie auf eine interne Repräsentation für datenintensive Workflows, dem sogenannten Prozessgraphenmodell (PGM), an, um die Datenverarbeitung eines datenintensiven Workflows zu optimieren. PGM erlaubt eine effiziente und sprachunabhängige Definition und Anwendung der Restrukturierungsregeln und unterstützt somit eine Optimierung von Datenverarbeitungsoperationen, die in unterschiedlichen Beschreibungssprachen definiert sein können. Die Regelbasis enthält Restrukturierungsregeln, die auf existierenden und neuen Optimierungsstrategien beruhen. Insbesondere nutzen die Restrukturierungsregeln das Wissen über Abhängigkeiten in einer Workflowbeschreibung aus, um die darin eingebetteten Datenverarbeitungsoperationen unter Beibehaltung der ursprünglichen Ausführungssemantik eines datenintensiven Workflows zu optimieren. Die Kontrollstrategie bestimmt, welche Restrukturierungsregeln in welcher Reihenfolge auf welche Teile einer Workflowbeschreibung angewendet werden, um zum einen das Optimierungspotential eines datenintensiven Workflows umfassend zu nutzen und zum anderen die Korrektheit der Regelanwendungen sicherzustellen. Die ausführliche Beschreibung des Prozessgraphenmodells, der Regelbasis und der Kontrollstrategie stehen im Mittelpunkt dieser wissenschaftlichen Abhandlung. Des Weiteren wird eine prototypische Implementierung des Optimierungsansatzes vorgestellt, welche dessen praktische Einsatzfähigkeit unterstreicht. Schließlich wird die Effektivität der einzelnen Restrukturierungsregeln mithilfe verschiedener Messszenarien untersucht. Dabei wird gezeigt, dass durch Anwendung der Restrukturierungsregeln Leistungssteigerungen in mehreren Größenordnungen erreicht werden können.Item Open Access Supporting multi-tenancy in Relational Database Management Systems for OLTP-style software as a service applications(2015) Schiller, Oliver; Mitschang, Bernhard (Prof. Dr.-Ing. habil.)The consolidation of multiple tenants onto a single relational database management system (RDBMS) instance, commonly referred to as multi-tenancy, turned out being beneficial since it supports improving the profit margin of the provider and allows lowering service fees, by what the service attracts more tenants. So far, existing solutions create the required multi-tenancy support on top of a traditional RDBMS implementation, i. e., they implement data isolation between tenants, per-tenant customization and further tenant-centric data management features in application logic. This is complex, error-prone and often reimplements efforts the RDBMS already offers. Moreover, this approach disables some optimization opportunities in the RDBMS and represents a conceptual misstep with Separation of Concerns in mind. For the points mentioned, an RDBMS that provides support for the development and operation of a multi-tenant software as a service (SaaS) offering is compelling. In this thesis, we contribute to a multi-tenant RDBMS for OLTP-style SaaS applications by extending a traditional disk-oriented RDBMS architecture with multi-tenancy support. For this purpose, we primarily extend an RDBMS by introducing tenants as first-class database objects and establishing tenant contexts to isolate tenants logically. Using these extensions, we address tenant-aware schema management, for which we present a schema inheritance concept that is tailored to the needs of multi-tenant SaaS applications. Thereafter, we evaluate different storage concepts to store a tenant’s tuples with respect to their scalability. Next, we contribute an architecture of a multi-tenant RDBMS cluster for OLTP-style SaaS applications. At that, we focus on a partitioning solution which is aligned to tenants and allows obtaining independently manageable pieces. To balance load in the proposed cluster architecture, we present a live database migration approach, whose design favors low migration overhead and provides minimal interruption of service.Item Open Access Contributions to low energy consumption in digital circuits(2000) Bühler, Markus; Baitinger, Utz G. (Prof. Dr.-Ing)After bipolar, static PMOS, and NMOS technologies have been widely replaced by static CMOS, static current has practically disappeared in digital circuits. Thus, the problem of power consumption was thought to be solved. However, with increasing integration densities and operation frequencies, combined with the advent of complex portable devices, design for low power has regained its importance as the third design goal, beside delay and area consumption. But in contrast to the past, today, dynamic power consumption is dominant by far. The domain of low power design can be divided into two major subdomains: power estimation and actual circuit design for low power, the latter including all efforts for power optimization and low power synthesis. In this thesis, specific aspects of both subdomains are treated on different levels. The design aspect is covered by an investigation of suitable circuit techniques for a novel, 3D, T-gate, SOI technology. It was found that DPL fits best the structural requirements of this technology but consumes 50 more power than static CMOS. The consequences are discussed in the text. The main focus of this thesis is put on power estimation techniques on gate level. A novel, set based simulation method is presented and extended for real delay gate models (RDM). Several further optimization methods are proposed. It is shown that the RDM extension can also be applied to bitparallel logic simulators. As a last extension the set based approach is combined with probabilistic simulation methods, thus making it possible to take into account signal correlations during probabilistic estimation.Item Open Access Information driven exploration in robotics(2016) Kulick, Johannes; Toussaint, Marc (Prof. Dr.)Imagine an intelligent robot entering an unknown room. It starts interacting with its new surroundings to understand what properties the new objects have and how they interact with each other. Finally, he gathered enough information to skillfully perform various tasks in the new environment. This is the vision behind our research towards intelligent robots. An important role in the described behavior is the ability to chose actions in order to learn new things. This ability we call exploration. It enables the robot to quickly learn about the properties of the objects. Surprisingly autonomous exploration has been mostly neglected by robotics research so far, because many fundamental problems like motor control and perception were still not satisfactory solved. The developments of recent years have, however, overcome this hurdle. State of the art methods enable us now to conduct research on exploration in robotics. On the other hand the machine learning and statistics community has developed methods and the theoretical background to lead learning algorithms to the most promising data. Under the terms active learning and experimental design many methods have been developed to improve the learning rate with fewer training data. In this thesis we combine results from both fields to develop a framework of exploration in robotics. We base our framework on the notion of information and information gain, developed in the field of information theory. And although we show that optimal exploration is a computational hard problem, we develop efficient exploration strategies using information gain as measure and Bayesian experimental design as foundation. To test the explorative behavior generated by our strategies we introduce the Physical Exploration Challenge. It formalizes the desired behavior as exploration of external degrees of freedom. External degrees of freedom are those the robot can not articulate directly but only by interacting with the environment. We present how we can model different exploration tasks of external degree of freedom: Exploring the meaning of geometric symbols by moving objects, exploring the existence of joints and their properties, and exploring how different joints in the environment are interdependent. Different robots show these exploration tasks in both simulated and real world experiments.Item Open Access Efficient code offloading techniques for mobile applications(2017) Berg, Florian; Rothermel, Kurt (Prof. Dr. rer. nat. Dr. h. c.)Since the release of the first smart phone from Apple in the year 2007, smart phones in general experience a fast growth of rising popularity. A smart phone typically possesses among others a touchscreen display as user interface, a mobile communication for accessing the Internet, and a System-on-a-Chip as an integrated circuit of required components like a central processing unit. This pervasive computing platform derives its required power from a battery, where an end user runs upon it different kinds of applications like a calendar application or a high-end mobile game. Differing in the usage of the local resources from a battery-operated smart phone, a heavy utilization of local resources like playing a resource-demanding application drains the limited resource of energy in few hours. Despite the constant increase of memory, communication, or processing capabilities of a smart phone since the release in 2007, applications are also getting more and more sophisticated and demanding. As a result, the energy consumed on a smart phone was, still is, and will be its main limiting factor. To prevent the limited resource of energy from a quick exhaustion, researchers propose code offloading for (resource-constrained) mobile devices like smart phones. Code offloading strives for increasing the energy efficiency and execution speed of applications by utilizing a server instance in the infrastructure. To this end, a code offloading approach executes dynamically resource-intensive parts from an application on powerful remote servers in the infrastructure on behalf of a (resource-constrained) mobile device. During the remote execution of a resource-intensive application part on a remote server, a mobile device only waits in idle mode until it receives the result of the application part executed remotely. Instead of executing an application part on its local resources, a (resource-constrained) mobile device benefits from the more powerful resources of a remote server by sending the information required for a remote execution, waiting in idle mode, and receiving the result of the remote execution. The process of offloading code from a (resource-constrained) mobile device to a powerful remote server in the infrastructure, however, faces different problems. For instance, code offloading introduces some overhead for additional computation and communication on a mobile device. Moreover, spontaneous disconnections during a remote execution can cause a higher energy consumption and execution time than a local execution on a mobile device without code offloading. To this end, this dissertation addresses the whole process of offloading code from a mobile device not only to one but also to multiple remote resources, comprising the following steps: 1) First, code offloading has to identify feasible parts from an application for a remote execution, where the distributed execution of the identified application part is more beneficial than its local execution. A feasible part for a remote execution typically has the following properties: A low size of information required for transmission before a remote execution, a resource-intensive computation not accessing local sensors, and a low size of information required for transmission after a remote execution. In the area of identification of application parts for a remote execution, this dissertation presents an approach based on code annotations from application developers that automatically transforms a monolithic execution on a mobile device to a distributed execution on multiple heterogeneous resources. In contrast to related approaches in the literature, the annotation-based approach requires least interventions from application developers and end users, keeping the overhead introduced on a mobile device low. 2) For an application part identified for a remote execution, code offloading has to determine its execution side, executing the application part either on the local resources of a mobile device or on the remote resource at the infrastructure. In the area of determining the execution side for an application part, this dissertation presents the offloading problem, where a mobile device decides whether to execute an application part locally or remotely. Furthermore, this dissertation also presents an approach called "code bubbling" that shifts the decision making into the infrastructure. In contrast to related approaches in the literature, the decision-based approach on a mobile device and the bubbling-based approach minimize the execution time, energy consumption, and monetary cost for an application. 3) To determine the execution side for an application part identified for a remote execution, code offloading has to obtain different parameters from the application, participating resources, and utilized links. In the area of obtaining the information required from an application, this dissertation presents a bit-flipping approach that dynamically flips a bit at the modification of application-related information. Furthermore, this dissertation also presents an offload-aware Application Programming Interface (API) that encapsulates the application-related information required for code offloading. In contrast to related approaches in the literature, the bit-flipping approach and the offload-aware API provide an efficient gathering of information at run-time, keeping the overhead introduced on a mobile device low. 4) Beside the information from an application, code offloading has to obtain further information from participating resources and utilized links. In the area of obtaining the information required from participating resources and utilized links, this dissertation presents the approach of code bubbling, already mentioned above. In contrast to related approaches in the literature, the bubbling-based approach makes the offload decision at the place where the related information occurs, keeping the overhead introduced on a mobile device, participating resources, and utilized links low. 5) In case of a remote execution of an application part, code offloading has to send the information required for a remote execution to the remote resource that subsequently executes the application part on behalf of the mobile device. In the area of sending the required information and executing an application part remotely, this dissertation presents code offloading with a cache on the remote side. The cache on the remote side serves as a collective storage of results for already executed application parts, avoiding a repeated execution of previously run application parts. In contrast to related approaches in the literature, the caching-aware approach increases the efficiency of code offloading, keeping the energy consumption, execution time, and monetary cost low. 6) While a remote resource executes an application part, code offloading has to handle the occurrence of failures like a failure of the remote resource or a disconnection. In the area of handling the occurrence of failures, this dissertation presents a preemptable offloading of code with safe-points. The preemptable offloading of code with safe-points enables an interruption of an offloading process and a corresponding continuation of a remote execution on a mobile device, without abandoning the complete result calculated remotely so far. Based on a preemptable offloading of code with safe-points, this dissertation further presents a predictive offloading of code with safe-points that minimizes the overhead introduced by safe-point'ing and maximizes the efficiency of a deadline-aware offloading. In contrast to related approaches in the literature, the preemptable approach with safe-point'ing increases the robustness of code offloading in case of failures. Furthermore, the predictive approach for safe-point'ing ensures a minimal responsiveness and a maximal efficiency of applications despite failures. 7) At the end of a remote execution of an application part, code offloading has to gather on the remote resource the required information after the execution and send this information to the mobile device. In the area of gathering the required information, a remote resource utilizes the same approaches as a mobile device, already mentioned above (cf. the bit-flipping approach and the offload-aware API). 8) Last, code offloading has to receive on the mobile device the information from a remote resource, install the information on the mobile device, and continue the execution of the application on the mobile device. In the area of installing the information and continuing the execution locally, a mobile device utilizes the approaches already mentioned above (cf. the bit-flipping approach and the offload-aware API).