• Journal of KIISE:Databases
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• v.35 no.1
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• pp.54-66
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• 2008

A spatio-temporal join is an expensive operation that is commonly used in spatio-temporal database systems. In order to generate an efficient query plan for the queries involving spatio-temporal join operations, it is crucial to estimate accurate selectivity for the join operations. Given two dataset $S_1,\;S_2$ of discrete data and a timestamp $t_q$, a spatio-temporal join retrieves all pairs of objects that are intersected each other at $t_q$. The selectivity of the join operation equals the number of retrieved pairs divided by the cardinality of the Cartesian product $S_1{\times}S_2$. In this paper, we propose aspatio-temporal histogram to estimate selectivity of spatio-temporal join by extending existing geometric histogram. By using a wide spectrum of both uniform dataset and skewed dataset, it is shown that our proposed method, called Spatio-Temporal Histogram, can accurately estimate the selectivity of spatio-temporal join. Our contributions can be summarized as follows: First, the selectivity estimation of spatio-temporal join for discrete data has been first attempted. Second, we propose an efficient maintenance method that reconstructs histograms using compression of spatial statistical information during the lifespan of discrete data.

• Journal of the Economic Geographical Society of Korea
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• v.16 no.2
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• pp.198-217
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• 2013

This research aims to examine the behavior changes of telemedicine participants with regard to time-space reconfiguration and to address the implications of telemedicine in terms of extensibility and restrictions (ambilaterality). According to the results of this research, telemedicine can lead to behavior changes in telemedicine participants, particularly patients. However, it is difficult to anticipate the time-space reconfiguration of telemedicine participants drastically. In other words, although telemedicine minimizes patients' burden of accessibility to and utilization of medical institutions, it requires the patients to visit medical institutions at least once due to the restricted application of telemedicine related to technological problems, the characteristics of medical practice and mutual stakes among the medical institutions involved in telemedicine. And physicians (telemedicine providers as mediators between medical specialists and patients) and medical specialists (as the ultimate telemedicine providers) do not evidence considerable changes in their behaviors, except for offline meetings for information sharing and medical training. Because the present telemedicine system does not require simultaneity between physicians, patients and medical specialists. Furthermore, present telemedicine operation is absorbed into existing medical activities as a health care delivery method. These phenomena are due to 1) the interests among medical institutions and the limitation or generalization of telemedicine technologies to stimulate regional-based telemedicine operation and 2) the goal of face-to-face interactions between patients and doctors, which is to avoid misdiagnosis and side effects. Finally, medical activities related to telemedicine do not differ from general medical activities. The ambilaterality of telemedicine in terms of extensibility and the restriction of time-space reconfiguration is an unsettled problem in the ICT technologies of medical services.