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Issue No. 05 - May (2013 vol. 25)
ISSN: 1041-4347
pp: 1097-1110
Jing Li , University of Hong Kong, Hong Kong
Yin David Yang , Advanced Digital Sciences Center, Singapore
Nikos Mamoulis , University of Hong Kong, Hong Kong
Given a set of spatial points $(DS)$, each of which is associated with categorical information, e.g., restaurant, pub, etc., the optimal route query finds the shortest path that starts from the query point (e.g., a home or hotel), and covers a user-specified set of categories (e.g., {pub, restaurant, museum}). The user may also specify partial order constraints between different categories, e.g., a restaurant must be visited before a pub. Previous work has focused on a special case where the query contains the total order of all categories to be visited (e.g., museum $(\rightarrow)$ restaurant $(\rightarrow)$ pub). For the general scenario without such a total order, the only known solution reduces the problem to multiple, total-order optimal route queries. As we show in this paper, this naïve approach incurs a significant amount of repeated computations, and, thus, is not scalable to large data sets. Motivated by this, we propose novel solutions to the general optimal route query, based on two different methodologies, namely backward search and forward search. In addition, we discuss how the proposed methods can be adapted to answer a variant of the optimal route queries, in which the route only needs to cover a subset of the given categories. Extensive experiments, using both real and synthetic data sets, confirm that the proposed solutions are efficient and practical, and outperform existing methods by large margins.
Scattering, Indexes, Greedy algorithms, Spatial databases, Complexity theory, Electronic mail, Trajectory, spatial databases, Query processing

Y. D. Yang, J. Li and N. Mamoulis, "Optimal Route Queries with Arbitrary Order Constraints," in IEEE Transactions on Knowledge & Data Engineering, vol. 25, no. , pp. 1097-1110, 2013.
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