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Geometric SpeedUp Techniques for Finding Shortest Paths in Large Sparse Graphs
, 2003
"... In this paper, we consider Dijkstra's algorithm for the single source single target shortest paths problem in large sparse graphs. The goal is to reduce the response time for online queries by using precomputed information. For the result of the preprocessing, we admit at most linear space. ..."
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Cited by 59 (15 self)
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In this paper, we consider Dijkstra's algorithm for the single source single target shortest paths problem in large sparse graphs. The goal is to reduce the response time for online queries by using precomputed information. For the result of the preprocessing, we admit at most linear space. We assume that a layout of the graph is given. From this layout, in the preprocessing, we determine for each edge a geometric object containing all nodes that can be reached on a shortest path starting with that edge. Based on these geometric objects, the search space for online computation can be reduced significantly. We present an extensive experimental study comparing the impact of different types of objects. The test data we use are traffic networks, the typical field of application for this scenario.
Drawing Graphs to Speed Up ShortestPath Computations
, 2005
"... We consider the problem of (repeatedly) computing singlesource singletarget shortest paths in large, sparse graphs. Previous investigations have shown the practical usefulness of geometric speedup techniques that guarantee the correctness of the result for shortestpath computations. However, such ..."
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Cited by 9 (3 self)
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We consider the problem of (repeatedly) computing singlesource singletarget shortest paths in large, sparse graphs. Previous investigations have shown the practical usefulness of geometric speedup techniques that guarantee the correctness of the result for shortestpath computations. However, such speedup techniques utilize a layout of the graph which typically comes from geographic information. This paper examines the question how geometric speedup techniques can be used in case there is no layout given. We present an extensive computational study analyzing the usefulness of methods from graph drawing as foundation for such techniques. It turns out that using appropriate layout algorithms, a significant speedup can be achieved.
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 Proceedings of TACAS’98
, 1998
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Geometric Shortest Path Containers
, 2004
"... In this paper, we consider Dijkstra's algorithm for the single source single target shortest path problem in large sparse graphs. The goal is to reduce the response time for online queries by using precomputed information. Due to the size of the graph, preprocessing space requirements can b ..."
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Cited by 2 (1 self)
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In this paper, we consider Dijkstra's algorithm for the single source single target shortest path problem in large sparse graphs. The goal is to reduce the response time for online queries by using precomputed information. Due to the size of the graph, preprocessing space requirements can be only linear in the number of nodes. We assume that a layout of the graph is given. In the preprocessing, we determine from this layout a geometric object for each edge containing all nodes that can be reached by a shortest path starting with that edge.
Towards a Conceptual and ServiceBased Adaptation Model
"... Abstract. Current practice in adaptation modeling assumes that concepts and relationships between concepts are the fundamental building blocks of any adaptive course or adaptive application. This assumption underlies many of the mismatches we nd between the syntax of an adaptation model and the sema ..."
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Cited by 1 (0 self)
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Abstract. Current practice in adaptation modeling assumes that concepts and relationships between concepts are the fundamental building blocks of any adaptive course or adaptive application. This assumption underlies many of the mismatches we nd between the syntax of an adaptation model and the semantics of the `realworld' entity it is trying to model, e.g. procedural knowledge modeled as a single concept and services or activities modeled as pockets of intelligent content. Furthermore, it results in adaptation models that are devoid of truly interactive services with work ow and data ow between those services; it is impossible to capture the semantics of a processoriented application, e.g. activitybased learning in education and Standard Operating Procedures (SOPs) in the workplace. To this end, we describe a representation of a conceptual and servicebased adaptation model. The most signi cant departure from existing representations for adaptation models is the rei cation of services. The goal is to allow for the adaptation of the process itself and not just its constituent parts, e.g. an SOP can be adapted to the role or job function of a user. This expressive power will address the mismatches identi ed above and allow for activitybased and processoriented adaptive applications. 1
Witness Validation and Stepwise Testification across Software Verifiers
"... It is commonly understood that a verification tool should provide a counterexample to witness a specification violation. Until recently, software verifiers dumped error witnesses in proprietary formats, which are often neither human nor machinereadable, and an exchange of witnesses between differ ..."
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It is commonly understood that a verification tool should provide a counterexample to witness a specification violation. Until recently, software verifiers dumped error witnesses in proprietary formats, which are often neither human nor machinereadable, and an exchange of witnesses between different verifiers was impossible. To close this gap in softwareverification technology, we have defined an exchange format for error witnesses that is easy to write and read by verification tools (for further processing, e.g., witness validation) and that is easy to convert into visualizations that conveniently let developers inspect an error path. To eliminate manual inspection of false alarms, we develop the notion of stepwise testification: in a first step, a verifier finds a problematic program path and, in addition to the verification result false, constructs a witness for this path; in the next step, another verifier reverifies that the witness indeed violates the specification. This process can have more than two steps, each reducing the state space around the error path, making it easier to validate the witness in a later step. An obvious application for testification is the setting where we have two verifiers: one that is efficient but imprecise and another one that is precise but expensive. We have implemented the technique of errorwitnessdriven program analysis in two stateoftheart verification tools, CPAchecker and Ultimate Automizer, and show by experimental evaluation that the approach is applicable to a large set of verification tasks.
International Workshop on Dynamic and Adaptive Hypertext: Generic Frameworks, Approaches and Techniques (DAH'09) Towards a Conceptual and ServiceBased Adaptation Model
"... Abstract. Current practice in adaptation modeling assumes that concepts and relationships between concepts are the fundamental building blocks of any adaptive course or adaptive application. This assumption underlies many of the mismatches we nd between the syntax of an adaptation model and the sema ..."
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Abstract. Current practice in adaptation modeling assumes that concepts and relationships between concepts are the fundamental building blocks of any adaptive course or adaptive application. This assumption underlies many of the mismatches we nd between the syntax of an adaptation model and the semantics of the `realworld' entity it is trying to model, e.g. procedural knowledge modeled as a single concept and services or activities modeled as pockets of intelligent content. Furthermore, it results in adaptation models that are devoid of truly interactive services with work ow and data ow between those services; it is impossible to capture the semantics of a processoriented application, e.g. activitybased learning in education and Standard Operating Procedures (SOPs) in the workplace. To this end, we describe a representation of a conceptual and servicebased adaptation model. The most signi cant departure from existing representations for adaptation models is the rei cation of services. The goal is to allow for the adaptation of the process itself and not just its constituent parts, e.g. an SOP can be adapted to the role or job function of a user. This expressive power will address the mismatches identi ed above and allow for activitybased and processoriented adaptive applications. 1