Efficient Computation of Group Skyline Queries on MapReduce

Skyline query is one of the important issues indatabase research and has been applied in diverse applicationsincluding multi-criteria decision support systems and so on. Theresponse of a skyline query eliminates unnecessary tuples andreturns only the user-interested result. Traditional skyline querypicks out the outstanding tuples, based on one-to-one recordcomparisons. Some modern applications request, beyond thesingular ones, for superior combinations of records. For example,fantasy basketball is composed of 5 players, fantasy baseball of 9players, and a hackathon of several programmers. Group skylineaims at considering all the groups comprising several records,and finding out the non-dominated ones. Because of the highcomplexity, few studies have been conducted and none has beenpresented in either distributed or parallel computing. This paperis the first study that solves the group skyline in the distributedMapReduce framework. We propose the MRGS algorithm togenerate all the combinations, compute the winners at each localnode, and find out the answer globally. We further propose theMRIGS algorithm to release the bottleneck of MRGS onunbalanced computing load of nodes. Finally, we propose theMRIGS-P algorithm to prune the impossible combinations andproduce indexed and balanced MapReduce computation.Extensive experiments with NBA datasets show that MRIGS-P is6 times faster than the MRGS algorithm

Seismic Fragility Analysis for Sheet Pile Wharves — Case Study of the Hualien Harbor in Taiwan

The seismic fragility curves represent the conditional probabilities that the structural damage meets or exceeds the specified damage states at various levels of the ground motion parameters, such as peak ground acceleration (PGA). In this study, the seismic fragility analysis for the sheet pile wharves of the Hualien Harbor in Taiwan was performed. The finite element analysis software PLAXIS was adopted for the nonlinear dynamic analysis. The time histories of several representative earthquake events that actually occurred in Taiwan, including the 1999 Chi-Chi Earthquake, were scaled to various PGA levels as the input motions. Then the seismic responses of the sheet pile wharves subjected to these earthquakes of different intensities were obtained. It is assumed that the maximum residual displacement at the top of the sheet pile wall is lognormal distributed. Thus, the conditional exceedance probabilities of each specified damage state at different levels of PGA were estimated according to the displacement threshold value of each damage state, and the fragility curves were deduced. Moreover, these fragility curves were parameterized assuming they can be well approximated by the lognormal cumulative probability function, which is important for the rapid estimation of earthquake loss