Universität Stuttgart
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Item Open Access Visualization of uncorrelated point data(2008) Reina, Guido; Ertl, Thomas (Prof. Dr.)Sciences are the most common application context for computer-generated visualization. Researchers in these areas have to work with large datasets of many different types, but the one trait that is common to all is that in their raw form they exceed the cognitive abilities of human beings. Visualization not only aims at enabling users to quickly extract as much information as possible from datasets, but also at allowing the user to work at all with those that are too large and complex to be directly grasped by human cognition. In this work, the focus is on uncorrelated point data, or point clouds, which is sampled from real-world measurements or generated by computer simulations. Such datasets are gridless and exhibit no connectivity, and each point represents an entity of its own. To effectively work with such datasets, two main problems must be solved: on the one hand, a large number of complex primitives with potentially many attributes must be visualized, and on the other hand the interaction with the datasets must be designed in an intuitive way. This dissertation will present novel methods which allow the handling of large, point-based data sets of high dimensionality. The contribution for the rendering of hundreds of thousands of application-specific glyphs is a Graphics-Processing-Unit(GPU)-based solution that allows the exploration of datasets that exhibit a moderate number of dimensions, but an extremely large number of points. These approaches are proven to be working for molecular dynamics(MD) datasets as well as for 3D tensor fields. Factors critical for the performance of these algorithms are thoroughly analyzed, the main focus being on the fast rendering of these complex glyphs in high quality. To improve the visualization of datasets with many attributes and only a moderate number of points, methods for the interactive reduction of dimensionality and analysis of the influences of different dimensions as well as of different metrics will be presented. The rendering of the resulting data in 3D similarity space is also addressed. A GPU-based reduction of dimensions has been implemented that allows interactive tweaking of the reduction parameters while observing the results in real time. With the availability of a fast and responsive visualization, the missing component for a complete system is the human-computer interaction. The user must be able to navigate the information space and interact with a dataset, selecting or filtering the items that are of interest to him, inspecting the attributes of particular data points. Today, one must distinguish between the application context and the modality of different interaction approaches. Current research ranges from keyboard-and-mouse desktop interaction over different haptic interfaces (also including feedback) up to tracked interaction for virtual reality(VR) installations. In the context of this work, the problem of interacting with point-based datasets is tackled for two different situations. The first is the workstation-based analysis of clustering mechanics in thermodynamics simulations, the second a VR immersive navigation and interaction with point cloud datasets.Item Open Access Multi-field visualization on graphics processing units(2008) Botchen, Ralf Peter; Ertl, Thomas (Prof. Dr.)The generation of multi-field data has become commonplace in many scientific disciplines and application areas today. While researchers have produced numerous techniques for analyzing a single scalar, vector, or tensor field over the last years, finding approaches for exploring multi-field datasets still forms one of the significant challenges in visualization and analytics. One crucial aspect for the growing demand of multi-field visualization techniques is the fact that scientists need to explore the interaction of these fields to gain deeper understanding of underlying processes and relationships. This work addresses the challenge of illustrating multi-field data and presents new approaches of visualization techniques for a variety of application areas, with the aim to map these algorithms to graphics hardware architectures to achieve interactive visualization. In particular, the main contributions of this thesis contain multi-field flow visualization with one focus on integrating an additional flow uncertainty value, based on measurement simulation, into visualization. Therefore, texture based advection techniques are extended for the transport and display of the additional information. The second focus lies on the illustration of multiple fields as one combined characteristic set to minimize memory usage and allow further feature extraction from the new unique representation. New techniques are developed for multi-field volume rendering in the area of medical applications, with the primary challenge to intermix volumetric data that was acquired by different medical imaging modalities. The proposed solutions give implementation details for raycasting and slice-based rendering of multiple overlapping volumes. The third application area is video visualization. This domain is a typical representative for multi-field visualization, as it combines both, flow fields and multi-volume data for illustration. The goal of the introduced video visualization techniques is to extract dynamic or still objects in a scene, detect their individual actions and the relations among each other and to display this filtered information as a continuous stream of signatures for analysis. Another problematic issue in multi-field visualization is the size of the data, which is usually rather large. Yet, data transfer to and memory size on GPUs are two major bottlenecks. To address this issue, throughout the thesis techniques for data reduction by combination and data bricking for continuous streaming are discussed. Finally, multi-field data encoding and visualization techniques are presented that utilize the advantages of radial basis functions to minimize the data size.Item Open Access A comprehensive model of usability(2008) Winter, Sebastian; Wagner, Stefan; Deißenböck, FlorianUsability is a key quality attribute of successful software systems. Unfortunately, there is no common understanding of the factors influencing usability and their interrelations. Hence, the lack of a comprehensive basis for designing, analyzing, and improving user interfaces. This paper proposes a 2-dimensional model of usability that associates system properties with the activities carried out by the user. By separating activities and properties, sound quality criteria can be identified, thus facilitating statements concerning their interdependencies. This model is based on a tested quality meta-model that fosters preciseness and completeness. A case study demonstrates the manner by which such a model aids in revealing contradictions and omissions in existing usability standards. Furthermore, the model serves as a central and structured knowledge base for the entire quality assurance process, e.g. the automatic generation of guideline documents.Item Open Access Abstract syntax of WS-BPEL 2.0(2008) Kopp, Oliver; Mietzner, Ralph; Leymann, FrankWS-BPEL 2.0 is the current version of the "Business Process Execution Language for Web Services". Until now, no formal definition of its syntax exists. We present a complete syntax of WS-BPEL 2.0 of both abstract and executable processes.Item Open Access Particle tracing methods for visualization and computer graphics(2008) Schafhitzel, Tobias; Weiskopf, Daniel (Prof. Dr.)This thesis discusses the broad variety of particle tracing algorithms with focus on flow visualization. Starting with a general overview of the basics of visualization and computer graphics, mathematics, and fluid dynamics, a number of methods using particle tracing for flow visualization and computer graphics are proposed. The first part of this thesis considers mostly texture-based techniques that are implemented on the graphics processing unit (GPU) in order to provide an interactive dense representation of 3D flow fields. This part considers particle tracing methods that can be applied on general vector fields and includes texture based visualization in volumes as well as on surfaces. Furthermore, it is described how particle tracing can be used for extracting flow structures, like path surfaces, of the given vector field. The second part of this thesis considers particle tracing on derived vector fields for flow visualization. Therefore, first a feature extraction criterion is applied on a fluid flow field. In most cases this results in a scalar field serving as base for the particle tracing methods. Here, it is shown how higher order derivatives of scalar fields can be used to extract flow features like 1D vortex core lines or 2D shear sheets. The extracted structures are further processed in terms of feature tracking. The third part generalizes particle tracing for arbitrary applications in visualization and computer graphics. Here, the particles' path either might be defined by the perspective of the human eye or by a force field that influences the particles' motion by considering second order ordinary differential equations. All three parts clarify the importance of particle tracing methods for a wide range of applications in flow visualization and computer graphics by various examples. Furthermore, it is shown how the flexibility of this method strongly depends on the underlying vector field, and how those vector fields can be generated in order to solve problems that go beyond traditional particle tracing in fluid flow fields.Item Open Access Supporting business process fragmentation while maintaining operational semantics : a BPEL perspective(2008) Khalaf, Rania; Leymann, Frank (Prof. Dr.)Globalization and the increase of competitive pressures created the need for agility in business processes, including the ability to outsource, offshore, or otherwise distribute its once-centralized business processes or parts thereof. While hampered thus far by limited infrastructure capabilities, the increase in bandwidth and connectivity and decrease in communication cost have removed these limits. An organization that aims for such fragmentation of its business processes needs to be able to separate the process into different parts. Today, this is a manual, design-time endeavor. For example, it may use the concept of subprocesses as parts to be outsourced. However, there is often no way to foresee, in advance, which parts of the process need to be cut-off. Thus, today’s technology for outsourcing is static and not dynamic at all. Therefore, there is a growing need for the ability to fragment one’s business processes in an agile manner, and be able to distribute and wire these fragments so that their combined execution recreates the function of the original process. Additionally, this needs to be done in a networked environment, which is where ‘Service Oriented Architecture’ plays a vital role. ‘Service Oriented Architecture’ (SOA) is a relatively new approach to software that natively deals with the very dynamic, distributed, loosely coupled, and heterogeneous features of today’s networked environment, offering application functions as networked services. Web services is one instantiation of an SOA, consisting of a modular, layered stack of XML standards and corresponding implementations that address the different aspects of this environment. The standard covering business processes for Web services is the Business Process Execution Language for Web Services (also known as ‘BPEL’). Relevant characteristics of BPEL are that it is SOA-centric, has a scope construct that groups activities providing them with common behavior such as fault and compensation handlers, and combines graph and calculus based approaches to process modeling. This thesis describes how to identify, create, and execute process fragments without loosing the operational semantics of the original process models. It does so within the framework of the Web services stack of standards, BPEL in particular. The contributions are a categorization of existing Web services aggregation techniques, a meta-model of Web services business process mechanisms using a graph-based formalism, a solution for the automatic and operational semantics-preserving decomposition of such processes, and an architecture and implementation for a corresponding build-time and runtime environment.Item Open Access WS-BPEL extension for semantic web services (BPEL4SWS), version 1.0(2008) Karastoyanova, Dimka; Van Lessen, Tammo; Leymann, Frank; Nitzsche, Joerg; Wutke, DanielThe Web Services Business Process Execution Language, version 2.0 (WS-BPEL 2.0 or BPEL for brevity) introduces a model for business processes based on Web services. A BPEL process orchestrates interactions among different Web services. The language encompasses features needed to describe complex control flows, including error handling and compensation behavior. BPEL for Semantic Web Services (BPEL4SWS) uses Semantic Web Service Frameworks to define a communication channel between two partner services instead of using the partner link which is based on WSDL 1.1. It enables describing activity implementations in a much more flexible manner based on ontological descriptions of service requesters and providers.Item Open Access A cross-layer framework for sensor networks(2008) Lachenmann, Andreas; Rothermel, Kurt (Prof. Dr.)Cross-layer interactions are often used in wireless sensor networks. They help to optimize energy consumption, deal with memory limitations, and consider the special properties of wireless communication. However, cross-layer interactions have the disadvantage of negatively affecting desirable properties of the software design like modularity and reusability. In the extreme, applications consist of a monolithic piece of code that is hard to develop and impossible to maintain. Therefore, this thesis investigates different approaches to address the negative side-effects of cross-layer interactions. In particular, it develops a framework that pursues three different strategies. First, it tries to preserve modularity and increase reusability by decoupling components that exchange data. This strategy is realized by TinyXXL, a programming abstraction for cross-layer data exchange. This part of the framework has been created based on an analysis of cross-layer interactions in existing applications. With some compile-time optimizations TinyXXL can reduce both energy and memory consumption compared to an application built from reusable components. Using Neidas, a novel neighborhood data sharing algorithm, it offers a comprehensive system for data exchange among the layers of a single node and with neighboring nodes. Second, the framework relaxes one of the constraints that often lead to cross-layer interactions and, thus, reduces the need to apply them. Specifically, it includes ViMem, a flash-based virtual memory system that helps to reduce memory limitations and tries to optimize the memory layout. Finally, the third strategy is to partially move energy concerns into the system software. For this purpose the framework includes Levels, an abstraction to specify optional functionality which allows to accurately meet a user-defined lifetime goal. If necessary, Levels deactivates functionality in order to reach that target lifetime. Furthermore, it includes a distributed algorithm that helps to provide a constant application quality over the total network lifetime.Item Open Access Clone detection in automotive model-based development(2008) Deißenböck, Florian; Hummel, Benjamin; Juergens, Elmar; Schätz, Bernhard; Wagner, Stefan; Girard, Jean-François; Teuchert, StefanModel-based development is becoming an increasingly common development methodology. In important domains like embedded systems already major parts of the code are generated from models specified with domain-specific modelling languages. Hence, such models are nowadays an integral part of the software development and maintenance process and therefore have a major economic and strategic value for the software-developing organisations. Nevertheless almost no work has been done on a quality defect that is known to seriously hamper maintenance productivity in classic code-based development: Cloning. This paper presents an approach for the automatic detection of clones in large models as they are used in model-based development of control systems. The approach is based on graph theory and hence can be applied to most graphical data-flow languages. An industrial case study demonstrates the applicability of our approach for the detection of clones in Matlab/Simulink models that are widely used in model-based development of embedded systems in the automotive domain.Item Open Access Analyse und Optimierung der Softwareschichten von wissenschaftlichen Anwendungen für Metacomputing(2008) Keller, Rainer; Resch, Michael (Prof. Dr.-Ing.)Für parallele Anwendungen ist das Message Passing Interface (MPI) das Programmierparadigma der Wahl für Höchstleistungsrechner mit verteiltem Speicher. Mittels des Konzeptes des MetaComputings wiederum können verschiedenste Rechenressourcen mit PACX-MPI gekoppelt werden. Dies ist einerseits von Interesse, weil Problemgrößen gelöst werden sollen, die nicht auf nur einem System ausgeführt werden könnten, andererseits, weil gekoppelte Simulationen gerechnet werden, die auf bestimmten Rechnerarchitekturen ausgeführt werden sollen oder weil Systeme mit bestimmten Eigenschaften wie Visualisierungs- mit parallelen Rechenressourcen verbunden werden müssen. Diese Koppelung stellt für die verteilten Anwendungen eine Barriere dar, da Kommunikation zu nicht-lokalen Prozessen weitaus langsamer ist, als über das rechnerinterne Netzwerk. In dieser Arbeit werden Lösungen auf den Software-Ebenen ausgehend von der Netzwerkschicht, durch Verbesserungen innerhalb der verwendeten Middleware, bis hin zur Optimierung innerhalb der Anwendungsschicht erarbeitet. In Bezug auf die unterste Softwareschicht wird für die Middleware PACX-MPI eine allgemeine Bibliothek zur Netzwerkkommunikation auf Basis von User Datagram Protocol (UDP) entwickelt. Somit können Limitierungen des Transport Control Protocols (TCP) umgangen werden, vor allem in Verbindung mit Netzwerken mit hoher Latenz und großer Bandbreite, so genannte Long Fat Pipes. Die hier implementierte Bibliothek ist portabel programmiert und durch die Verwendung von Threads effizient. Dieses Protokoll erreicht gute Werte für die Bandbreite im Local Area Network (LAN), aber auch im Wide Area Network (WAN). Getestet wird dieses Protokoll zur Veranschaulichung mittels einer Verbindung zwischen Rechnern in Stuttgart und Canberra, Australien. Innerhalb der Middleware wird die Optimierung der kollektiven Kommunikationsroutinen behandelt und am Beispiel der Funktion PACX_Alltoall die Verbesserung anhand des IMB Benchmarks auf einem Metacomputer gezeigt. Zur Analyse der Kommunikationseigenschaften wird die Erweiterung einer Tracing-Bibliothek für PACX-MPI, sowie die Implementierung einer generischen Schnittstelle zur Messung der Kommunikationscharakteristik auf MPI-Schicht erläutert. Weiterhin wird eine allgemeine MPI-Testsuite vorgestellt, die beim Auffinden von Fehlern sowohl in PACX-MPI, als auch innerhalb der Open MPI Implementierung hilfreich war. Auf der obersten Softwareschicht werden Optimierungsmöglichkeiten für Anwendungen für MetaComputing aufgezeigt. Beispielhaft wird die Analyse des Kommunikationsmusters einer Anwendung aus dem Bereich der Bioinformatik gezeigt. Weiterhin wird die Implementierung des Cachings und Prefetchings von vielfach kommunizierten Daten mit räumlicher und zeitlicher Lokalität vorgestellt. Erst die Methodik des Cachings und Prefetchings erlaubt die Ausführung der Anwendung in einem Metacomputer und ist exemplarisch für eine Klasse von Algorithmen mit ähnlichem Kommunikationsmuster.