Mehdi Sharifzadeh
Cyrus Shahabi
Abstract
In this article, we first introduce the concept of Spatial Skyline Queries (SSQ). Given a set of data points P and a set of query points Q, each data point has a number of derived spatial attributes each of which is the point's distance to a query point. An SSQ retrieves those points of P which are not dominated by any other point in P considering their derived spatial attributes. The main difference with the regular skyline query is that this spatial domination depends on the location of the query points Q. SSQ has application in several domains such as emergency response and online maps. The main intuition and novelty behind our approaches is that we exploit the geometric properties of the SSQ problem space to avoid the exhaustive examination of all the point pairs in P and Q. Consequently, we reduce the complexity of SSQ search from O(|P|2|Q|) to O(|S|2|C| + √|P|), where |S| and |C| are the solution size and the number of vertices of the convex hull of Q, respectively.
Considering Euclidean distance, we propose two algorithms, B2S2 and VS2, for static query points and one algorithm, VCS2, for streaming Q whose points change location over time (e.g., are mobile). VCS2 exploits the pattern of change in Q to avoid unnecessary recomputation of the skyline and hence efficiently perform updates. We also propose two algorithms, SNS2 and VSNS2, that compute the spatial skyline with respect to the network distance in a spatial network database. Our extensive experiments using real-world datasets verify that both R-tree-based B2S2 and Voronoi-based VS2 outperform the best competitor approach in terms of both processing time and I/O cost. Furthermore, their output computed based on Euclidean distance is a good approximation of the spatial skyline in network space. For accurate computation of spatial skylines in network space, our experiments showed the superiority of VSNS2 over SNS2.
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Digital Library
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Index Terms
- Processing spatial skyline queries in both vector spaces and spatial network databases
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Reviews
Fatma Mili
Increasingly, various contexts call for queries where one is seeking a set of objects (points) from the database that form a skyline (no other point dominates them). These queries have been dubbed skyline queries. They are specified through a set of points ( qi ) that are then used as a basis to define the criterion of dominance and select the points of interest ( pj ). For example, given a set of agent locations ( qi ), find a set of potential restaurants ( pj ) where they could meet; given a set of explosion locations ( qi ), find the buildings ( pj ) that must be evacuated first; or, given a set of compromised nodes in a network, identify the nodes that must be isolated first. In many of these applications, the dominance relationship is exclusively spatial. Branch-and-bound algorithms have been introduced to address the general skyline query problem, without being restricted to spatial criteria. Sharifzadeh et al. focus on skyline queries where the points pj and qi have coordinates in space and where the dominance relationship is based on proximity to the query points qi . They establish geometric relationships that enable them to reduce the search space and derive two different algorithms that are more efficient than the general-purpose skyline query algorithms. They further address the case where the query points qi are mobile (for example, agents are moving); they develop a dynamic algorithm that minimizes the amount of computation required to update the skyline as the query points move. Finally, they address applications where the query criterion is not based on Euclidean distance (for example, weights on network edges), and thus does not benefit from the same geometric properties as the spatial queries. For these, they introduce two alternative approaches. In our increasingly mobile computing infrastructure, the problem addressed in this paper is of highly practical utility. Finding efficient and accurate algorithms to solve it is critical. I found the paper easy to read. The theoretical foundation is fairly straightforward, and it is exploited in very innovative and interesting ways throughout the paper. Online Computing Reviews Service
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