Contributions published at Department of Informatics (Burkhard Stiller)

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In the last ten years, software processes and software process improvement have been recognized as fundamental constituents for the development and maintenance of quality software. Much effort has been devoted to the development of models and standards for software processes, process maturity determination and process improvement. This article gives an introduction to the concepts of software processes and process improvement and presents an overview of models and standards in this field. First, we introduce the principles of process-oriented software development and discuss both advantages and risks. Then we give an overview of software process models and standards. In a second part, we present the concept of process improvement and illustrate the basic improvement cycle. Finally, we survey models and standards for software process improvement.

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During the past decade a new class of systems has emerged, which plays an important role in the support of efficient business process implementation: workflow systems. Despite their proliferation however, workflow systems are still being developed in an ad hoc way without making use of advanced software engineering technologies such as component-based system development and reuse of architecture artifacts.This work proposes a modern approach to workflow system construction. The approach is centered around a domain-specific software architecture metamodel (the REWORK metamodel) and a repository-based composition framework for workflow system construction out of reusable reactive components. The architecture metamodel defines the component and connector abstractions necessary for describing the static and dynamic aspects of a workflow system. The composition framework defines the lifecycle of a workflow system and supports the dynamic extension of a kernel workflow management system with application-specific elements. Appropriately, resulting systems are called REWORK systems.An event- and repository-based style underlies the REWORK framework. Events are the only component integration mechanism used in REWORK systems. Repositories support both system development by storing artifacts which are used for workflow system development and system operation by making explicit the structure of a running REWORK system.The iterative workflow system composition lifecycle proposed in this thesis comprises the following phases: the architecture analysis phase allows the identification and characterization of processing entities which participate in workflow execution; this phase is supported by a classification framework for processing entities in accordance to their integration-related properties. During the architecture definition phase workflow system components are defined and their behavior is tailored to specifications of workflows which are intended to be executed by the resulting system; furthermore, organizational relations and task assignment policies for these components are declaratively defined. The implementation phase is largely automated and consists in the instantiation of the defined components on top of an event-based operational infrastructure.As already mentioned the entire lifecycle is supported by repositories which store the workflow system artifacts. The iterative development comes into the picture once existing workflow systems have to be maintained either by adding new repository artifacts or by modifying existing ones. Thus, we dedicate a part of this thesis to the description of these repositories.

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Due to the relatively low X-ray intensities recommended for cranial Computed Tomography (CT), metallic implants such as dental fillings or orthodontic devices cause massive star-shaped artifacts in resultant CT images which hamper detailed diagnostics when planning cranio-maxillofacial surgery. Due to the geometry of the artifacts, important information is destroyed both near dental fillings and in the periphery of the image. To reduce surgery time, it has become common practice to use custom-designed stereolithographic (SL) 3D copies of skulls for pre-operational planning. However, 2D image artifacts result in 3D spikes in the stereolithographic model, making it virtually useless. Thus, prior to model production, metal-induced artifacts must be eluninated. This research work has developed a powerful and universal artifact reduction framework, which can be applied for a wide variety of artifact source constellations in the field of cranio-maxillofacial CT scans. As implementation platform for this artifact reduction framework the image processing tool Khoros was used. The basis for the artifact reduction framework is a CT simulator environment, which was implemented using state-of-the-art programming concepts (e.g. modularity, visual programming, multiprocessing, open-source, human computer interaction, etc.). The Khoros based CT simulator provides a powerful, expandable, and low-cost platform for further research in the field of artifact reduction. The new image processing based artifact reduction methods, which were developed and implemented in this research, are embedded into this CT simulator environment. With the implemented CT simulation environment it is possible to perform automated artifact reduction on complete patient CT data sets. Because of the black-box concept, provided by the developed CT simulator environment, the artifact reduction framework can be easily integrated into the diagnostic routine in the all-day clinical environment. The new artifact reduction algorithms, developed in this study, provide adequate artifact reduction results for a wide variety of artifact source constellations; especially for the applications 3D model building and diagnostics in the periphery of dental fillings. The main advantage of the new developed artifact reduction algorithms is the fact that instead of CT raw data, which is hard to acquire, CT image data can be used as source data to perform artifact reduction.

Information is widely considered one of the most important resources in the information age. Appropriate access to information is becoming increasingly important. This increase in the importance of information is accompanied by a dramatic increase in the amount of available information. Sophisticated information retrieval techniques have been developed that allow for efficient search and retrieval of specific documents from large document collections. Similar techniques are increasingly used in to support users in searching for all kinds of information. The widespread idea is that users have so-called information needs and that they utilize computers in order to satisfy these information needs. It is assumed that the user’s information needs can be modeled in such a way that computers can be used to automate the search for appropriate information. In this thesis, I argue that the concept of searching for information as a particular activity is based on the so-called rationalistic perspective. In this perspective, it is assumed that the basic mechanisms underlying human cognition and those underlying the functioning of computer systems are essentially the same. Recent results from research in cognitive science and, in particular, “situated cognition” , suggest that the principles underlying human cognition and those underlying data- processing in computers are fundamentally different. According to the situated cognition perspective, it is inappropriate to describe human cognition as a sequence of well-defined steps. Rather, cognition is fundamentally a continuous process. Based on this particular understanding of cognition, I argue for a new perspective on human information seeking. According to this perspective, information seeking is not a particular activity occurring in specific search situations but a permanently occurring process that is highly interactive and inherently situated. Indeed, the concept of searching as a specific activity ceases to exist when investigated in detail and thus seems to be artificially constructed. This does not mean, however, that searching as a specific activity does not exist at all but that searching is often simplified and “rationalized” when described as goal-directed search. In addition, the situated perspective explains why the scope of rational approaches to information-seeking support is limited: they are efficient in retrieving specific well-defined information but they can hardly cope with the situated aspects of information seeking. Based on the understanding of information seeking as situated activity, I discuss a conceptual framework for the development of tools that support situated information seeking. This framework adopts the notion of “scaffolding minds”, i.e., the understanding that the human mind depends to a large extent on its capability to transform complex “information-processing tasks” into simpler associative tasks by exploiting structures of the real world and by actively re-structuring problems into series of simpler problems so that they better fit the capabilities of human cognition. The focus of the framework is not on the efficient retrieval of specific information but on exploitation and the structuring of the social as well as the physical environment of the information seeker in order to simplify the access to information services and information. The framework is illustrated by three examples that I developed or supervised in the context of this thesis. The examples indicate a variety of promising ways to support situated information seeking by structuring the physical as well as the social environment in an appropriate way. However, the approaches also indicate that structuring the social environment is different from well-defined tasks, such as programming a computer. Social competence is required in order to exploit the full potential of the social environment as the members of the social environment have to be willing to support others in accessing information.

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