Contributions published at Department of Informatics (Burkhard Stiller)

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The subject of this thesis is rooted in two research areas, data security and database technology. Data security is concerned with the confidentiality, integrity and availability of data. It is related to database technology, because database management systems (DBMS) were developed in order to manage large amounts of data (which are shared by various users and application programs) in a secure and reliable way. Access control is a particular security measure which ensures that data are only accessed by authorised users. It was already provided by early DBMS like IBM's IMS or System R. However, new database technologies cause new security problems, which must be countered with appropriate access control mechanisms. In this thesis, two new dimensions of database technology are considered, the extension of data models (object-oriented DBMS) and the federation of existing, autonomous database systems. Access control problems that additionally arise in such environments (compared with classical, record-based DBMS) are presented, requirements on access control models are identified, and existing solutions are evaluated against these requirements. This evaluation motivates the model presented in this thesis. The subsequently suggested access control model is based on a formal object-oriented data model that includes all features which are usually found in commercial object-oriented systems. This data model is used to identify the protection objects and actions of the access control model. The global part of the model (to be applied at the federation layer) supports various concepts in the area of identity-based access control. It includes an elaborate role concept and a powerful authorisation paradigm. The global model is integrated with heterogeneous local (identity-based) access control models, such that authorisation autonomy of component systems is preserved. In particular, the coupling layer is able to propagate global authorisations to the involved component systems. Note that not access rights but authorisations are propagated. Since propagated authorisations can be rejected by a component system (due to local autonomy), the coupling layer provides for appropriate failure handling protocols. The access control model leads to a reference architecture to implement access control in a federated DBMS. This architecture is based upon a configurable global reference monitor (which implements the global access control model and supports different access control policies), a distribution monitor (which coordinates the propagation of global authorisations to component systems), a set of coupling modules for each kind of component system (which encapsulate the heterogeneous local models under a well-defined interface), and an application programming interface in order to integrate the access control system with a DBMS. The feasibility of the proposed solutions was demonstrated by implementing a prototypical system, called Argos'. The coupling approach is exemplified for Oracle (version 7.1) and the UNIX file protection system (SunOS 4.1.3).

In the study of adaptive behavior, autonomous mobile robots (“autonomous agents”) are meanwhile accepted as an useful research tool for gaining insight into the mechanisms underlying the behavior of natural systems. A second objective of autonomous agent research is to improve upon the state-of-the-art in engineering, in particular robotics, by incorporating design principles discovered in natural systems into the design of autonomous mobile robots. This thesis focuses on the latter objective. In autonomous agent research, the fact that animals gain much behavioral competence from dedicated peripheral structures, exploiting physical processes and analog signal processing properties, has been largely neglected so far. This is a problem because such structures are necessary for performing the kind of signal processing required for the agent to optimally interact with its environment. In this thesis it is shown that information contained in the physical structures of autonomous agents can be effectively extracted using analog signal processing techniques, allowing the agent to accomplish its given task. The method is to apply biologically inspired (neuromorphic) structures to the peripheral layer of autonomous agents, and perform real-world experiments, examining the behavioral competencies of the agents. This approach contrasts with typical robot control methods, in which information processing is performed after digitizing the peripheral signals, thereby potentially discarding information contained in the physical structure and the signal processing properties of the peripheral device. A number of case studies which investigate peripheral processing in autonomous agents are presented. The first one demonstrates that the morphology of a mobile robot can be exploited for performing a particular task (heap building) without using a dedicated control module for the task. Such kind of behavior can also be observed in certain ant species which served as inspiration source for these experiments. The second case study describes the development of polarization sensitive sensors. These sensors mimic the crossed-analyzer configuration discovered in certain insects. The outstanding advantage of this configuration is that the orientation of the perceived polarized light is measured independent of the ambient light intensity over a large dynamic range. The experimental results indicate that this neuromorphic peripheral structure can be successfully used in a celestial compass, providing directional clues for an autonomous mobile robot. The third study elaborates upon a single-chip analog sensory-motor VLSI device, which facilitates both sensor-signal processing and motor control for an autonomous mobile robot. The chip incorporates a number of neuromorphic engineering techniques, including an artificial retina and a dual feedback motor controller, allowing the agent to accomplish its linefollowing task. This implementation is based entirely on analog peripheral computing demonstrating the feasibility of robot control without the use of digital computing techniques. The fourth one discusses attention-based navigation applying controllable local sensitivity in an array of retina pixels on a silicon chip. This property is used for conditioning a particular steering direction preference for a mobile robot. In this implementation, the agent can control its peripheral device for extracting appropriate information from the retina output signal in which the visual attention-signal is encoded. The specific advantage of this realization is that there is no additional computational module necessary for obtaining the attention information. In the final study, landmark navigation using a dedicated peripheral structure implemented in analog VLSI is discussed. The objective of this development is to create a landmark navigation system based on a widely accepted model for insect navigation. In this model, the insect memorizes the scene at an important location (e.g. its nest) and uses the stored image for finding its way back to this location. With the chip is demonstrated that the algorithm describing this model can be implemented on a single peripheral device, relieving other processing modules within the agent from such computation. The experimental results demonstrate that information contained in dedicated physical peripheral structures can be exploited for achieving behavioral competencies in autonomous agents. Such mechanisms are of great importance for autonomous mobile robots because they help reduce energy consumption and improve the real-time performance of the agent. Moreover in this manner, the total computational burden of the system is distributed over a number of processing units acting in parallel, resulting in improved robustness of the system. Hence, equipping autonomous agents with structures, whose designs are based on principles discovered for peripheral signal processing in natural systems, is a very promising approach for creating intelligent behaving systems.

The field of “New Artificial Intelligence” (New AI) has been established over the last few years. This field has provided scientists and engineers with new ways of thinking about intelligent systems. One of the core insights of “New AI” is that the system-environment interaction plays a central role in the understanding and design of intelligent systems. This concept also referred to as embodiment has been manifested in the research methodology of the new field where the main goal is to build autonomous agents, i.e., autonomous robots, that are capable of interacting with the real world. Probably the most important type of agent-environment interaction is introduced by the agent’s movement within its environment. The ability to navigate from one place to another is very crucial for autonomous agents. Traditional AI approaches to the navigation problem were based on the concept of a world model. Such a system would perceive the world, update its internal world model, generate a plan in terms of actions that have to be performed, and execute these actions. It is doubtful whether this approach will ever lead to systems which are capable of robust navigation in complex real-world environments. There are several reasons for being pessimistic. First, because such systems are already extremely complex compared to the tasks they have to perform. Second, because they require large amounts of computational and memory resources. And third, because they lack the robustness required in the real world. This thesis presents a new way of designing and building agents, capable of navigating in real-world environments, based on biological findings. The goal is twofold, first to demonstrate that mechanisms which are thought to be employed by natural systems can be implemented in real-world artifacts, and second, to show that such mechanisms, though very parsimonious, are sufficient for achieving complex behavior. We call these agents biorobotic agents.

Virtual Reality (VR) environments offer a new kind of human computer as well as human human interaction. The user of a VR system can immerse himself into a computer-generated, multi-sensory, intuitively operable virtual experience space, and interact with virtual objects in real-time. In this thesis, a new model for the description and classification of VR systems is presented. The discussion of basic issues and challenges in the development, operation and maintenance of VR systems leads to a set of new approaches for VR application models and systems. The coupling of VR based systems with conventional database subsystems leads to a new architecture model for VR based information systems. This opens the potential for the design and implementation of very promising new application scenarios such as VR based geographic, medical, or facility information systems at large. Another interesting specific application field is found in tourism. A scenario that has hardly been discussed within the VR community yet. Until now, existing tourist information systems can not sufficiently meet the information-intensive, multimedia, and spatial nature of tourism related services and processes. The application of VR based tourist information systems can significantly contribute to the implemen tation of more appropriate solutions. By the help of a new methodology for systematic analysis and evaluation of VR systems, the system architecture, design rationales, and implemented user interface metaphors of three VR application prototypes will be presented and discussed. These are accompanied by system performance and usability experiments. The first prototype, a Virtual Realiy based Geographic Information System, implements sophisticated methods and techniques for efficient data management in real-time by applying a client-server architecture. They allow the dynamic loading of virtual environment data at runtime and optimize load strategies for increased runtime performance. User interface aspects of VR applications are discussed with the help of the other two protoypes, a cockpit based immersive driving simulator and a VR based holiday house exploration environment. Furthermore, a new software architecture is proposed to improve the integration of additional peripheral devices into an existing VR system environment and to enable the development of software components in parallel. The close relationship of the three application prototypes to the field of tourism allows one to apply the findings to the design of architecture models and user interface metaphors for VR based tourist information systems.

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One of the key advantages of information technology is its ability to support new organizational forms. The task of shifting between old and new forms, however, can be a difficult, time consuming, and haphazard process (Davenport, 1993, Davenport and Stoddard, 1994; Hammer, 1990). Interactions among various work practices can lead to numerous unanticipated side effects as mangers alter individual practices without considering whole systems of work. In particular, the importance of complementarities among different practices has been formalized mathematically in the economic literature (Milgrom and Roberts, 1990). However, practicing managers and students have had difficult in applying these insights.

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Bürgerinformation erlebt derzeit eine Renaissance in deutschen Städten, weil die Kommunen das Internet als ein Medium zur elektronischen Informationsbereitstellung entdecken. Eine empirische Untersuchung zeigt, daß die meisten Städte noch am Experimentieren sind und Bürgerinformation noch nicht bedarfsgerecht bereitstellen. Der Artikel gibt deshalb politische, organisatorische und technische Gestaltungshinweise dafür, die zu einer besseren elektronischen Bürgerinformation führen sollen. Zum Schluß werden mit einem Negativ-Szenario und einem Positiv-Szenario dargestellt, wie die elektronische Bürgerinformation in einer Informationsgesellschaft aussehen kann.