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Mining association rules in relational databases is a significant computational task with lots of applications. A fundamental ingredient of this task is the discovery of sets of attributes (itemsets) whose frequency in the data exceeds some threshold value. In this paper we describe two algorithms for completing the calculation of frequent sets using a tree structure for storing partial supports, called interim‐support (IS) tree. The first of our algorithms (T‐Tree‐First (TTF)) uses a novel tree pruning technique, based on the notion of (fixed‐prefix) potential inclusion, which is specially designed for trees that are implemented using only two pointers per node. This allows to implement the IS tree in a space‐efficient manner. The second algorithm (P‐Tree‐First (PTF)) explores the idea of storing the frequent itemsets in a second tree structure, called the total support tree (T‐tree); the main innovation lies in the use of multiple pointers per node, which provides rapid access to the nodes of the T‐tree and makes it possible to design a new, usually faster, method for updating them. Experimental comparison shows that these techniques result in considerable speedup for both algorithms compared with earlier approaches that also use IS trees (Principles of Data Mining and Knowledge Discovery, Proceedings of the 5th European Conference, PKDD, 2001, Freiburg, September 2001 (Lecture Notes in Artificial Intelligence, vol. 2168). Springer: Berlin, Heidelberg, 54–66; Journal of Knowledge‐Based Syst. 2000; 13 :141–149). Further comparison between the two new algorithms, shows that the PTF is generally faster on instances with a large number of frequent itemsets, provided that they are relatively short, whereas TTF is more appropriate whenever there exist few or quite long frequent itemsets; in addition, TTF behaves well on instances in which the densities of the items of the database have a high variance. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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We study deterministic gossiping in ad hoc radio networks with large node labels. The labels (identifiers)
of the nodes come from a domain of size N which may be much larger than the size n of the network (the number of nodes). Most
of the work on deterministic communication has been done for the model with small labels which assumes N = O(n). A notable
exception is Peleg's paper, where the problem of deterministic communication in ad hoc radio networks with large labels is
raised and a deterministic broadcasting algorithm is proposed, which runs in O(n2log n) time for N polynomially large in n. The O(nlog2n)-time deterministic broadcasting algorithm for networks with small labels given by Chrobak et al. implies deterministic
O(n log N log n)-time broadcasting and O(n2log2N log n)-time gossiping in networks with large labels. We propose two new deterministic gossiping algorithms for ad hoc radio
networks with large labels, which are the first such algorithms with subquadratic time for polynomially large N. More specifically,
we propose: a deterministic O(n3/2log2N log n)-time gossiping algorithm for directed networks; and a deterministic O(n log2N log2n)-time gossiping algorithm for undirected networks. 相似文献
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We study a recently introduced path coloring problem with applications to wavelength assignment in all-optical networks with
multiple fibers. In contrast to classical path coloring, it is, in this setting, possible to assign a color more than once
to paths that pass through the same edge; the number of allowed repetitions per edge is given and the goal is to minimize
the number of colors used.
We present algorithms and hardness results for tree topologies of special interest. Our algorithms achieve approximation ratio
of 2 in spiders and 3 in caterpillars, whereas the best algorithm for trees so far, achieves an approximation ratio of 4.
We also study the directed version of the problem and show that it admits a 3-approximation algorithm in caterpillars, while
it can be solved exactly in spiders.
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Grontas Panagiotis Pagourtzis Aris 《International Journal of Information Security》2023,22(4):819-832
International Journal of Information Security - Everlasting privacy protects cryptographic voting systems against the weakening of intractability assumptions on which they may be based. We find... 相似文献
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