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Hash Join Based Spatial Collocation Pattern Mining

Boiński P, Zakrzewicz M.

Foundations of Computing and Decision Sciences

2011

Vol. 36, No. 1

3-15

Every day, new and existing spatial databases, are populated by data from sensors, satellites and other devices providing spatial references. In this enormous flow of data, valuable and interesting patterns can be hidden. For researchers, one of the common tasks is to discover spatial collocations, i.e. subsets of spatial features that are frequently located together in space. The most widely known algorithm has been proposed by Shekhar et al. It is based on a step of spatial neighborhood materialization and a join-less generation of candidate instances, which are filtered in the remaining algorithm steps. We identified one of these steps to be a potential bottleneck of the algorithm. In this paper, we address the problem of efficient filtering of non clique instances and we propose to expand this task by applying hash join techniques. We have implemented and tested the aforementioned solution and shown that it results in better performance of the algorithm.

A Dichotomic Search Algorithm for Mining and Learning in Domain-Specific Logics

Ferré S., King R. D.

Fundamenta Informaticae

2005

Vol. 66, nr 1,2

1--32

Many application domains make use of specific data structures such as sequences and graphs to represent knowledge. These data structures are ill-fitted to the standard representations used in machine learning and data-mining algorithms: propositional representations are not expressive enough, and first order ones are not efficient enough. In order to efficiently represent and reason on these data structures, and the complex patterns that are related to them, we use domain-specific logics. We show these logics can be built by the composition of logical components that model elementary data structures. The standard strategies of top-down and bottom-up search are ill-suited to some of these logics, and lack flexibility. We therefore introduce a dichotomic search strategy, that is analogous to a dichotomic search in an ordered array. We prove this provides more flexibility in the search, while retaining completeness and non-redundancy. We present a novel algorithm for learning using domain specific logics and dichotomic search, and analyse its complexity. We also describe two applications which illustrates the search for motifs in sequences; where these motifs have arbitrary length and length-constrained gaps. In the first application sequences represent the trains of the East-West challenge; in the second application they represent the secondary structure of Yeast proteins for the discrimination of their biological functions.