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Hierarchical encoded path views for path query processing: An optimal model and its performance evaluation
 IEEE Transactions on Knowledge and Data Engineering
, 1998
"... Abstract—Efficient path computation is essential for applications such as intelligent transportation systems (ITS) and network routing. In ITS navigation systems, many path requests can be submitted over the same, typically huge, transportation network within a small time window. While path precompu ..."
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Cited by 86 (2 self)
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Abstract—Efficient path computation is essential for applications such as intelligent transportation systems (ITS) and network routing. In ITS navigation systems, many path requests can be submitted over the same, typically huge, transportation network within a small time window. While path precomputation (path view) would provide an efficient path query response, it raises three problems which must be addressed: 1) precomputed paths exceed the current computer main memory capacity for large networks; 2) diskbased solutions are too inefficient to meet the stringent requirements of these target applications; and 3) path views become too costly to update for large graphs (resulting in outofdate query results). We propose a hierarchical encoded path view (HEPV) model that addresses all three problems. By hierarchically encoding partial paths, HEPV reduces the view encoding time, updating time and storage requirements beyond previously known path precomputation techniques, while significantly minimizing path retrieval time. We prove that paths retrieved over HEPV are optimal. We present complete solutions for all phases of the HEPV approach, including graph partitioning, hierarchy generation, path view encoding and updating, and path retrieval. In this paper, we also present an indepth experimental evaluation of HEPV based on both synthetic and real GIS networks. Our results confirm that HEPV offers advantages over alternative path finding approaches in terms of performance and space efficiency. Index Terms—Path queries, path view materialization, hierarchical path search, GIS databases, graph partitioning. 1
A survey of parallel execution strategies for transitive closure and logic programs
 DISTRIBUTED AND PARALLEL DATABASES
, 1993
"... An important feature of database technology of the nineties is the use of parallelism for speeding up the execution of complex queries. This technology is being tested in several experimental database architectures and a few commercial systems for conventional selectprojectjoin queries. In particu ..."
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Cited by 24 (6 self)
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An important feature of database technology of the nineties is the use of parallelism for speeding up the execution of complex queries. This technology is being tested in several experimental database architectures and a few commercial systems for conventional selectprojectjoin queries. In particular, hashbased fragmentation is used to distribute data to disks under the control of different processors in order to perform selections and joins in parallel. With the development of new query languages, and in particular with the definition of transitive closure queries and of more general logic programming queries, the new dimension of recursion has been added to query processing. Recursive queries are complex; at the same time, their regular structure is particularly suited for parallel execution, and parallelism may give a high efficiency gain. We survey the approaches to parallel execution of recursive queries that have been presented in the recent literature. We observe that research on parallel execution of recursive queries is separated into two distinct subareas, one focused on the transitive closure of Relational Algebra expressions, the other one focused on optimization of more general Datalog queries. Though the subareas seem radically different because of the approach and formalism used, they have many common features. This is not surprising, because most typical Datalog queries can be solved by means of the transitive closure of simple
Hierarchical Path Views: A Model Based on Fragmentation and Transportation Road Types
, 1995
"... Efficient path query processing necessary for route guidance has been identified as one of the key requirements for Intelligent Transportation Systems (ITS) applications. While precomputing the view of all shortest paths provides the most efficient path retrieval, the view maintenance and storage co ..."
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Cited by 14 (5 self)
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Efficient path query processing necessary for route guidance has been identified as one of the key requirements for Intelligent Transportation Systems (ITS) applications. While precomputing the view of all shortest paths provides the most efficient path retrieval, the view maintenance and storage costs become unrealistic for large ITS networks. Based on ITS road type classification, we propose a hierarchical path view approach, in which the path view maintenance and storage costs are dramatically reduced at the cost of negligible loss of path optimality. Comparing with the traditional ITS path finding approaches that use A or hierarchical A , our hierarchical approach is superior in three areas: 1) path search is more efficient, 2) the connecting point from the lowlevel roads to the highlevel roads and vice versa are dynamically determined based on the most recent traffic, 3) within one region, the highlevel traffic can be dynamically rerouted through the lowlevel roads. In ...
Exploring Load Balancing in Parallel Processing of Recursive Queries
, 1996
"... Recent work on load balancing has confirmed its importance when one wants to achieve good performances during the actual evaluation of parallel database queries. Existing work mostly focuses on the join processing for parallel relational databases. We are interested here in more complex queries, suc ..."
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Cited by 6 (5 self)
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Recent work on load balancing has confirmed its importance when one wants to achieve good performances during the actual evaluation of parallel database queries. Existing work mostly focuses on the join processing for parallel relational databases. We are interested here in more complex queries, such as recursive ones. The main difference is that, in the latter case, the work due to a task cannot be previously determined and, consequently, no method can define at the outset the tasks to be executed in parallel in order to balance the workload at each processor. We propose a dosedriven dynamic strategy that aims at obtaining an improved workload balance and better use of the available resources. We examine the applicability of our strategy with its specialization to the case of the transitive closure query. Preliminary computational results on randomly generated test problems illustrate the efficiency of the proposed method. Keywords: Load Balancing, Dynamic Assignment, Recursive Quer...
An Experimental Study on Transitive Closure Representations
"... We present two new compact transitive closure representations. The first uses intervals and the second chains to store the closure. Both representations are based on previous methods designed for acyclic graphs. The new representations are applicable to all kinds of graphs, and can be efficiently co ..."
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Cited by 1 (0 self)
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We present two new compact transitive closure representations. The first uses intervals and the second chains to store the closure. Both representations are based on previous methods designed for acyclic graphs. The new representations are applicable to all kinds of graphs, and can be efficiently constructed during a single traversal of the input graph. We compared experimentally the average size of these representations and traditional list based representations. The inputs were random graphs. The interval representation outperformed the other representations: it typically required a space at most linear to the number of vertices of the input graph. The chain representation did not save much space compared to a list representation. We also studied the complexity of constructing the interval representation. Our results indicate that in the models of random graphs that we used, the transitive closure can typically be computed in a time linear to the size of the input graph when the interv...
A Hierarchical Path View Model for Path Finding in Intelligent Transportation Systems
 Journal of GeoInformatica
, 1997
"... Effective path ®nding has been identi®ed as an important requirement for dynamic route guidance in Intelligent Transportation Systems (ITS). Path ®nding is most ef®cient if the allpair (shortest) paths are precomputed because path search requires only simple lookups of the precomputed path views. S ..."
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Cited by 1 (1 self)
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Effective path ®nding has been identi®ed as an important requirement for dynamic route guidance in Intelligent Transportation Systems (ITS). Path ®nding is most ef®cient if the allpair (shortest) paths are precomputed because path search requires only simple lookups of the precomputed path views. Such an approach however incurs path view maintenance (computation and update) and storage costs which can be unrealistically high for large ITS networks. To lower these costs, we propose a Hierarchical Path View Model (HPVM) that partitions an ITS road map, and then creates a hierarchical structure based on the road type classi®cation. HPVM includes a map partition algorithm for creating the hierarchy, path view maintenance algorithms, and a heuristic hierarchical path ®nding algorithm that searches paths by traversing the hierarchy. HPVM captures the dynamicity of traf®c change patterns better than the ITS path ®nding systems that use the hierarchical A * approach because: (1) during path search, HPVM traverses the hierarchy by dynamically selecting the connection points between two levels based on uptodate traf®c, and (2) HPVM can reroute the highspeed road traf®c through local streets if needed. In this paper, we also present experimental results used to benchmark HPVM and to compare HPVM with alternative ITS path ®nding approaches, using both synthetic and real ITS maps that include a large Detroit map ( 4 28,000 nodes). The results show that the HPVM incurs much lower costs in path view maintenance and storage than the nonhierarchical path precomputation approach, and is more ef®cient in path search than the traditional ITS path ®nding using A * or hierarchical A * algorithms.
Transitive closure algorithm DISK_TC and its performance analysis
"... We present a new algorithm for computing the full transitive closure of a binary relation. We analyze its averagecase performance experimentally in an environment where secondary memory (disk) must be used to store the data. We compare our new algorithm, called disk tc, with the algorithm btc desi ..."
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We present a new algorithm for computing the full transitive closure of a binary relation. We analyze its averagecase performance experimentally in an environment where secondary memory (disk) must be used to store the data. We compare our new algorithm, called disk tc, with the algorithm btc designed by Ionnadis et al. [26] and reported by them to be the most efficient algorithm in disk memory environment. We present both quantitative and qualitative results showing that disk tc is faster than btc. In our analysis, we simulate the disk I/O in the main memory. Simulation takes less time than measuring a real system that does actual disk I/O; thus we can study a large number of inputs. We present also our analysis method and tools, which are applicable to other algorithm performance studies. Copyright c fl Vesa Hirvisalo, Esko Nuutila, and Eljas SoisalonSoininen. All rights reserved. TKOB135 ISBN 951223386X ISSN 12396893 TKK OFFSET 1 1 Introduction This paper presents a new...
An Efficient Path Computation Model for Hierarchically Structured
"... Abstract—In this paper, we have developed a HiTi (Hierarchical MulTi) graph model for structuring large topographical road maps to speed up the minimum cost route computation. The HiTi graph model provides a novel approach to abstracting and structuring a topographical road map in a hierarchical fas ..."
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Abstract—In this paper, we have developed a HiTi (Hierarchical MulTi) graph model for structuring large topographical road maps to speed up the minimum cost route computation. The HiTi graph model provides a novel approach to abstracting and structuring a topographical road map in a hierarchical fashion. We propose a new shortest path algorithm named SPAH, which utilizes HiTi graph model of a topographical road map for its computation. We give the proof for the optimality of SPAH. Our performance analysis of SPAH on grid graphs showed that it significantly reduces the search space over existing methods. We also present an indepth experimental analysis of HiTi graph method by comparing it with other similar works on grid graphs. Within the HiTi graph framework, we also propose a parallel shortest path algorithm named ISPAH. Experimental results show that inter query shortest path problem provides more opportunity for scalable parallelism than the intra query shortest path problem. Index Terms—Shortest Path, digital road maps, grid graphs, parallel shortest path computation, HiTi graph model.
Minimum Cost Path for a Shared Nothing Architecture
, 2004
"... Abstract: Computing the minimum cost path is a key requirement in Intelligent Transportation Systems (ITS) and in some Geographical Information Systems (GIS) applications. The major characteristics of these systems are the facts that the underlying transportation graph is large in size and the compu ..."
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Abstract: Computing the minimum cost path is a key requirement in Intelligent Transportation Systems (ITS) and in some Geographical Information Systems (GIS) applications. The major characteristics of these systems are the facts that the underlying transportation graph is large in size and the computation is under time constraint. Due to the insufficiency of the classic algorithms under these settings, recent studies have focused on speeding the computation by employing alternative techniques such as heuristics, precomputation and parallelization. In this study, we investigate solutions assuming a shared nothing architecture (i. e., Teradata multimedia database system) as a way of speeding up the computation further. We build our algorithms on a recently developed graph model, Hierarchical mulTigraph (HiTi), and describe both concurrent and parallel versions of the algorithms. The concurrent algorithm allows simultaneous exploration of the search space by utilizing dynamically created agents across multiple disk nodes, which is efficiently supported by the Teradata multimedia database system architecture. The parallel algorithm breaks the problem into a set of smaller subproblems by exploiting a set of intermediate nodes that the shortest path passes through. We also investigate the impact of replicating subgraphs in the performance of our algorithms. We evaluated our algorithms via a simulation study and demonstrated that our concurrent and parallel algorithms show almost a linear speedup as the number of disk/CPU nodes is increased. Concurrent algorithm exhibits better sizeup, and scaleup results than the parallel algorithm.