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.

Abstract not found

In many fields of application shortest path finding problems in very large graphs arise. Scenarios where large numbers ofonW##O queries for shortest paths have to be processedin real-time appear for examplein tra#cinc5###HF5 systems.In such systems, the techn5Ww# con sidered to speed up the shortest pathcomputation are usually basedon precomputed incomputed5 On approach proposedoften in thiscon text is a spacereduction where precomputed shortest paths are replaced by sin## edges with weight equal to thelenOq of the corresponres shortest path.In this paper, we give a first systematic experimen tal study of such a spacereduction approach. Wein troduce theconOkW of multi-level graph decomposition Foron specificapplication scenica from the field of timetable information in public tranc ort, we perform a detailed anai ysisan experimen tal evaluation of shortest path computation based on multi-level graph decomposition.

Computing a shortest path from one node to another in a directed graph is a very common task in practice. This problem is classically solved by Dijkstra's algorithm. Many techniques are known to speed up this algorithm heuristically, while optimality of the solution can still be guaranteed. In most studies, such techniques are considered individually.

Using a set of geometric containers to speed up shortest path queries in a weighted graph has been proven a useful tool for dealing with large sparse graphs. Given a layout of a graph G = (V, E), we store, for each edge (u, v) E, the bounding box of all nodes t V for which a shortest u-t-path starts with (u, v). Shortest path queries can then be answered by Dijkstra's algorithm restricted to edges where the corresponding bounding box contains the target.

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 on-line 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.

Speed-up techniques that exploit given node coordinates have proven useful for shortest-path computations in transportation networks and geographic information systems. To facilitate the use of such techniques when coordinates are missing from some, or even all, of the nodes in a network we generate artificial coordinates using methods from graph drawing. Experiments on a large set of German train timetables indicate that the speed-up achieved with coordinates from our drawings is close to that achieved with the true coordinates—and in some special cases even better.

Today a large variety of services is available to everyone who has appropriate access to the internet. Open Service Markets (OSM) with a multitude of service types, service providers and service customers have come into being. Because of the large number of participating entities it can be assumed that certain services are offered by different service providers at the same time, but differing in their service quality. A core issue for OSMs is the question how service providers and service customers come together and how the interaction between them takes place. Most approaches are based on the trading concept and are dedicated to a single service use only. Based on an analysis of the OSM model we sketch the Service Supplier Relation (SSR) model supporting the repetitive use of services on a long-term basis. We have drawn inspiration from subcontracting industry which is widely accepted e.g. in the automotive industry. After discussing the SSR model we briefly describe the concept of Vi...

Current approaches for service mediation, such as trading, do not provide means for a long-term binding of services. They do not ensure that certain services are provided and that the desired service properties are fulfilled. Moreover, a server may withdraw a service offer at any time. For the integration of external services into an enterprise internal service market, it is necessary to guarantee the permanent availability of the services with desired properties and to sustain these properties. This requires that the technical relationship between service provider and customer has to be extended by commercial and legal ones. In this paper, we introduce the concept of Virtual Private Resources to enable long-term relationships between the customer and the provider of a service. Virtual Private Resources are services that can be bound by contract for a longer period of time. They can be considered as private ones, although the physical resources that provide the service may change or be...