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The development of self-adaptive software requires the engineering of an adaptation engine that controls and adapts the underlying adaptable software by means of feedback loops. The adaptation engine often describes the adaptation by using runtime models representing relevant aspects of the adaptable software and particular activities such as analysis and planning that operate on these runtime models. To systematically address the interplay between runtime models and adaptation activities in adaptation engines, runtime megamodels have been proposed for self-adaptive software. A runtime megamodel is a specific runtime model whose elements are runtime models and adaptation activities. Thus, a megamodel captures the interplay between multiple models and between models and activities as well as the activation of the activities. In this article, we go one step further and present a modeling language for ExecUtable RuntimE MegAmodels (EUREMA) that considerably eases the development of adaptation engines by following a model-driven engineering approach. We provide a domain-specific modeling language and a runtime interpreter for adaptation engines, in particular for feedback loops. Megamodels are kept explicit and alive at runtime and by interpreting them, they are directly executed to run feedback loops. Additionally, they can be dynamically adjusted to adapt feedback loops. Thus, EUREMA supports development by making feedback loops, their runtime models, and adaptation activities explicit at a higher level of abstraction. Moreover, it enables complex solutions where multiple feedback loops interact or even operate on top of each other. Finally, it leverages the co-existence of self-adaptation and off-line adaptation for evolution.
Interactive rendering techniques for focus+context visualization of 3D geovirtual environments
(2013)
This thesis introduces a collection of new real-time rendering techniques and applications for focus+context visualization of interactive 3D geovirtual environments such as virtual 3D city and landscape models. These environments are generally characterized by a large number of objects and are of high complexity with respect to geometry and textures. For these reasons, their interactive 3D rendering represents a major challenge. Their 3D depiction implies a number of weaknesses such as occlusions, cluttered image contents, and partial screen-space usage. To overcome these limitations and, thus, to facilitate the effective communication of geo-information, principles of focus+context visualization can be used for the design of real-time 3D rendering techniques for 3D geovirtual environments (see Figure). In general, detailed views of a 3D geovirtual environment are combined seamlessly with abstracted views of the context within a single image. To perform the real-time image synthesis required for interactive visualization, dedicated parallel processors (GPUs) for rasterization of computer graphics primitives are used. For this purpose, the design and implementation of appropriate data structures and rendering pipelines are necessary. The contribution of this work comprises the following five real-time rendering methods: • The rendering technique for 3D generalization lenses enables the combination of different 3D city geometries (e.g., generalized versions of a 3D city model) in a single image in real time. The method is based on a generalized and fragment-precise clipping approach, which uses a compressible, raster-based data structure. It enables the combination of detailed views in the focus area with the representation of abstracted variants in the context area. • The rendering technique for the interactive visualization of dynamic raster data in 3D geovirtual environments facilitates the rendering of 2D surface lenses. It enables a flexible combination of different raster layers (e.g., aerial images or videos) using projective texturing for decoupling image and geometry data. Thus, various overlapping and nested 2D surface lenses of different contents can be visualized interactively. • The interactive rendering technique for image-based deformation of 3D geovirtual environments enables the real-time image synthesis of non-planar projections, such as cylindrical and spherical projections, as well as multi-focal 3D fisheye-lenses and the combination of planar and non-planar projections. • The rendering technique for view-dependent multi-perspective views of 3D geovirtual environments, based on the application of global deformations to the 3D scene geometry, can be used for synthesizing interactive panorama maps to combine detailed views close to the camera (focus) with abstract views in the background (context). This approach reduces occlusions, increases the usage the available screen space, and reduces the overload of image contents. • The object-based and image-based rendering techniques for highlighting objects and focus areas inside and outside the view frustum facilitate preattentive perception. The concepts and implementations of interactive image synthesis for focus+context visualization and their selected applications enable a more effective communication of spatial information, and provide building blocks for design and development of new applications and systems in the field of 3D geovirtual environments.
Cost models are an essential part of database systems, as they are the basis of query performance optimization. Based on predictions made by cost models, the fastest query execution plan can be chosen and executed or algorithms can be tuned and optimised. In-memory databases shifts the focus from disk to main memory accesses and CPU costs, compared to disk based systems where input and output costs dominate the overall costs and other processing costs are often neglected. However, modelling memory accesses is fundamentally different and common models do not apply anymore. This work presents a detailed parameter evaluation for the plan operators scan with equality selection, scan with range selection, positional lookup and insert in in-memory column stores. Based on this evaluation, a cost model based on cache misses for estimating the runtime of the considered plan operators using different data structures is developed. Considered are uncompressed columns, bit compressed and dictionary encoded columns with sorted and unsorted dictionaries. Furthermore, tree indices on the columns and dictionaries are discussed. Finally, partitioned columns consisting of one partition with a sorted and one with an unsorted dictionary are investigated. New values are inserted in the unsorted dictionary partition and moved periodically by a merge process to the sorted partition. An efficient attribute merge algorithm is described, supporting the update performance required to run enterprise applications on read-optimised databases. Further, a memory traffic based cost model for the merge process is provided.
Companies strive to improve their business processes in order to remain competitive. Process mining aims to infer meaningful insights from process-related data and attracted the attention of practitioners, tool-vendors, and researchers in recent years. Traditionally, event logs are assumed to describe the as-is situation. But this is not necessarily the case in environments where logging may be compromised due to manual logging. For example, hospital staff may need to manually enter information regarding the patient’s treatment. As a result, events or timestamps may be missing or incorrect. In this paper, we make use of process knowledge captured in process models, and provide a method to repair missing events in the logs. This way, we facilitate analysis of incomplete logs. We realize the repair by combining stochastic Petri nets, alignments, and Bayesian networks. We evaluate the results using both synthetic data and real event data from a Dutch hospital.
Die Automatisierung von Geschäftsprozessen unterstützt Unternehmen, die Ausführung ihrer Prozesse effizienter zu gestalten. In existierenden Business Process Management Systemen, werden die Instanzen eines Prozesses völlig unabhängig voneinander ausgeführt. Jedoch kann das Synchronisieren von Instanzen mit ähnlichen Charakteristiken wie z.B. den gleichen Daten zu reduzierten Ausführungskosten führen. Zum Beispiel, wenn ein Onlinehändler zwei Bestellungen vom selben Kunden mit der gleichen Lieferanschrift erhält, können diese zusammen verpackt und versendet werden, um Versandkosten zu sparen. In diesem Papier verwenden wir Konzepte aus dem Datenbankbereich und führen Datensichten für Geschäftsprozesse ein, um Instanzen zu identifizieren, welche synchronisiert werden können. Auf Grundlage der Datensichten führen wir das Konzept der Batch-Regionen ein. Eine Batch-Region ermöglicht eine kontext-bewusste Instanzen-Synchronisierung über mehrere verbundene Aktivitäten. Das eingeführte Konzept wird mit einer Fallstudie evaluiert, bei der ein Kostenvergleich zwischen der normalen Prozessausführung und der Batchverarbeitung durchgeführt wird.
There are two common approaches to implement a virtual machine (VM) for a dynamic object-oriented language. On the one hand, it can be implemented in a C-like language for best performance and maximum control over the resulting executable. On the other hand, it can be implemented in a language such as Java that allows for higher-level abstractions. These abstractions, such as proper object-oriented modularization, automatic memory management, or interfaces, are missing in C-like languages but they can simplify the implementation of prevalent but complex concepts in VMs, such as garbage collectors (GCs) or just-in-time compilers (JITs). Yet, the implementation of a dynamic object-oriented language in Java eventually results in two VMs on top of each other (double stack), which impedes performance. For statically typed languages, the Maxine VM solves this problem; it is written in Java but can be executed without a Java virtual machine (JVM). However, it is currently not possible to execute dynamic object-oriented languages in Maxine. This work presents an approach to bringing object models and execution models of dynamic object-oriented languages to the Maxine VM and the application of this approach to Squeak/Smalltalk. The representation of objects in and the execution of dynamic object-oriented languages pose certain challenges to the Maxine VM that lacks certain variation points necessary to enable an effortless and straightforward implementation of dynamic object-oriented languages' execution models. The implementation of Squeak/Smalltalk in Maxine as a feasibility study is to unveil such missing variation points.
Scalable compatibility for embedded real-time components via language progressive timed automata
(2013)
Die korrekte Komposition individuell entwickelter Komponenten von eingebetteten Realzeitsystemen ist eine Herausforderung, da neben funktionalen Eigenschaften auch nicht funktionale Eigenschaften berücksichtigt werden müssen. Ein Beispiel hierfür ist die Kompatibilität von Realzeiteigenschaften, welche eine entscheidende Rolle in eingebetteten Systemen spielen. Heutzutage wird die Kompatibilität derartiger Eigenschaften in einer aufwändigen Integrations- und Konfigurationstests am Ende des Entwicklungsprozesses geprüft, wobei diese Tests im schlechtesten Fall fehlschlagen. Aus diesem Grund wurde eine Zahl an formalen Verfahren Entwickelt, welche eine frühzeitige Analyse von Realzeiteigenschaften von Komponenten erlauben, sodass Inkompatibilitäten von Realzeiteigenschaften in späteren Phasen ausgeschlossen werden können. Existierenden Verfahren verlangen jedoch, dass eine Reihe von Bedingungen erfüllt sein muss, welche von realen Systemen nur schwer zu erfüllen sind, oder aber, die verwendeten Analyseverfahren skalieren nicht für größere Systeme. In dieser Arbeit wird ein Ansatz vorgestellt, welcher auf dem formalen Modell des Timed Automaton basiert und der keine Bedingungen verlangt, die von einem realen System nur schwer erfüllt werden können. Der in dieser Arbeit vorgestellte Ansatz enthält ein Framework, welches eine modulare Analyse erlaubt, bei der ausschließlich miteinender kommunizierende Komponenten paarweise überprüft werden müssen. Somit wird eine skalierbare Analyse von Realzeiteigenschaften ermöglicht, die keine Bedingungen verlangt, welche nur bedingt von realen Systemen erfüllt werden können.
Enacting business processes in process engines requires the coverage of control flow, resource assignments, and process data. While the first two aspects are well supported in current process engines, data dependencies need to be added and maintained manually by a process engineer. Thus, this task is error-prone and time-consuming. In this report, we address the problem of modeling processes with complex data dependencies, e.g., m:n relationships, and their automatic enactment from process models. First, we extend BPMN data objects with few annotations to allow data dependency handling as well as data instance differentiation. Second, we introduce a pattern-based approach to derive SQL queries from process models utilizing the above mentioned extensions. Therewith, we allow automatic enactment of data-aware BPMN process models. We implemented our approach for the Activiti process engine to show applicability.
The new interactive online educational platform openHPI, (https://openHPI.de) from Hasso Plattner Institute (HPI), offers freely accessible courses at no charge for all who are interested in subjects in the field of information technology and computer science. Since 2011, “Massive Open Online Courses,” called MOOCs for short, have been offered, first at Stanford University and then later at other U.S. elite universities. Following suit, openHPI provides instructional videos on the Internet and further reading material, combined with learning-supportive self-tests, homework and a social discussion forum. Education is further stimulated by the support of a virtual learning community. In contrast to “traditional” lecture platforms, such as the tele-TASK portal (http://www.tele-task.de) where multimedia recorded lectures are available on demand, openHPI offers didactic online courses. The courses have a fixed start date and offer a balanced schedule of six consecutive weeks presented in multimedia and, whenever possible, interactive learning material. Each week, one chapter of the course subject is treated. In addition, a series of learning videos, texts, self-tests and homework exercises are provided to course participants at the beginning of the week. The course offering is combined with a social discussion platform where participants have the opportunity to enter into an exchange with course instructors and fellow participants. Here, for example, they can get answers to questions and discuss the topics in depth. The participants naturally decide themselves about the type and range of their learning activities. They can make personal contributions to the course, for example, in blog posts or tweets, which they can refer to in the forum. In turn, other participants have the chance to comment on, discuss or expand on what has been said. In this way, the learners become the teachers and the subject matter offered to a virtual community is linked to a social learning network.
Die neue interaktive Online-Bildungsplattform openHPI (https://openHPI.de) des Hasso-Plattner-Instituts (HPI) bietet frei zugängliche und kostenlose Onlinekurse für interessierte Teilnehmer an, die sich mit Inhalten aus dem Bereich der Informationstechnologien und Informatik beschäftige¬n. Wie die seit 2011 zunächst von der Stanford University, später aber auch von anderen Elite-Universitäten der USA angeboten „Massive Open Online Courses“, kurz MOOCs genannt, bietet openHPI im Internet Lernvideos und weiterführenden Lesestoff in einer Kombination mit lernunterstützenden Selbsttests, Hausaufgaben und einem sozialen Diskussionsforum an und stimuliert die Ausbildung einer das Lernen fördernden virtuellen Lerngemeinschaft. Im Unterschied zu „traditionellen“ Vorlesungsportalen, wie z.B. dem tele-TASK Portal (http://www.tele-task.de), bei dem multimedial aufgezeichnete Vorlesungen zum Abruf bereit gestellt werden, bietet openHPI didaktisch aufbereitete Onlinekurse an. Diese haben einen festen Starttermin und bieten dann in einem austarierten Zeitplan von sechs aufeinanderfolgenden Kurswochen multimedial aufbereitete und wann immer möglich interaktive Lehrmaterialien. In jeder Woche wird ein Kapitel des Kursthemas behandelt. Dazu werden zu Wochenbeginn eine Reihe von Lehrvideos, Texten, Selbsttests und ein Hausaufgabenblatt bereitgestellt, mit denen sich die Kursteilnehmer in dieser Woche beschäftigen. Kombiniert sind die Angebote mit einer sozialen Diskussionsplattform, auf der sich die Teilnehmer mit den Kursbetreuern und anderen Teilnehmern austauschen, Fragen klären und weiterführende Themen diskutieren können. Natürlich entscheiden die Teilnehmer selbst über Art und Umfang ihrer Lernaktivitäten. Sie können in den Kurs eigene Beiträge einbringen, zum Beispiel durch Blogposts oder Tweets, auf die sie im Forum verweisen. Andere Lernende können diese dann kommentieren, diskutieren oder ihrerseits erweitern. Auf diese Weise werden die Lernenden, die Lehrenden und die angebotenen Lerninhalte in einer virtuellen Gemeinschaft, einem sozialen Lernnetzwerk miteinander verknüpft.