Browsing by Author "Gat, Erann"

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    Reasoning about knowledge using extensional logics
    Gat, Erann (Virginia Polytechnic Institute and State University, 1987)
    When representing statements about knowledge in an extensional logic, it occasionally happens that undesired conclusions arise. Such extraneous conclusions are often the result of substitution of equals for equals or existential instantiation within intensional operators such as Know. In the past, efforts at solving this problem have centered on modifications to the logic. In this thesis, I propose a solution that leaves the logic intact and changes the representation of the statements instead. The solution presented here has four main points: 1) Only propositions can be known. 2) Relations rather than functions should be used to describe objects. 3) Temporal reasoning is often necessary to represent many real world problems. 4) In cases where more than one label can apply to the same object, an agent's knowledge about labels must be explicitly represented. When these guidelines are followed, statements about knowledge can be represented in standard first-order predicate logic in such a way that extraneous conclusions cannot be drawn. Standard first-order theorem provers (like Prolog) can then be used to solve problems which involve reasoning about knowledge
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    Reasoning About Knowledge Using Extensional Logics
    Gat, Erann; Miller, David P. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1987)
    When representing statements about knowledge in a extensional logic, it occasionally happens that undesired conclusions arise. Such extraneous conclusions are often the result of substitution of equals for equals or existential instantiation within intensional operators such as Know. In the past, efforts at solving this problem have centered on modifications to the logic. In this thesis, I propose a solution that leaves the logic intact and changes the representation of the statements instead. The solution presented here has four main points: 1) Only propositions can be known. 2) Relations rather than functions should be used to describe objects. 3) Temporal reasoning is often necessary to represent many real-world problems. 4) In cases where more than one label can apply to the same object, an agent's knowledge about labels must be explicitly represented. When these guidelines are followed, statements about knowledge can be represented in standard first-order predicate logic in such a way that extraneous conclusions cannot be drawn. Standard first-order theorem provers (like Prolog) can then be used to solve problems which involve reasoning about knowledge.
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    Reliable goal-directed reactive control of autonomous mobile robots
    Gat, Erann (Virginia Tech, 1991-04-19)
    This dissertation demonstrates that effective control of autonomous mobile robots in real-world environments can be achieved by combining reactive and deliberative components into an integrated architecture. The reactive component allows the robot to respond to contingencies in real time. Deliberation allows the robot to make effective predictions about the world. By using different computational mechanisms for the reactive and deliberative components, much existing deliberative technology can be effectively incorporated into a mobile robot control system. The dissertation describes the design and implementation of a reactive control system for an autonomous mobile robot which is explicitly designed to interface to a deliberative component A programming language called ALF A is developed to program this system. The design of a control architecture which incorporates this reactive system is also described. The architecture is heterogeneous and asynchronous, that is, it consists of components which are structured differently from one another, and which operate in parallel. This prevents slow deliberative computations from adversely affecting the response time of the overall system. The architecture produces behavior which is reliable and goal-directed, yet reactive to contingencies, in the face of noise, limited computational resources, and an unpredictable environment. The system described in this dissertation has been used to control three real robots and a simulated robot performing a variety of tasks in real-world and simulated real-world environments. A general design methodology based upon bottom-up hierarchical decomposition is demonstrated. The methodology is based on the principle of cognizant failure, that is, that low-level activities should be designed in a way as to detect failures and state transitions at high levels of abstraction. Furthermore, the results of deliberative computations should be used to guide the robot's actions, but not to control those actions directly.