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71.
Panos Vassiliadis Zografoula Vagena Spiros Skiadopoulos Nikos Karayannidis Timos Sellis 《Information Systems》2001,26(8)
Extraction-Transformation-loading (ETL) tools are pieces of software responsible for the extraction of data from several sources, their cleansing, customization and insertion into a data warehouse. Literature and personal experience have guided us to conclude that the problems concerning the ETL tools are primarily problems of complexity, usability and price. To deal with these problems we provide a uniform metamodel for ETL processes, covering the aspects of data warehouse architecture, activity modeling, contingency treatment and quality management. The ETL tool we have developed, namely
, is capable of modeling and executing practical ETL scenarios by providing explicit primitives for the capturing of common tasks.
provides three ways to describe an ETL scenario: a graphical point-and-click front end and two declarative languages: XADL (an XML variant), which is more verbose and easy to read and SADL (an SQL-like language) which has a quite compact syntax and is, thus, easier for authoring. 相似文献
72.
Machine Translation of arbitrary input is difficult,but the output quality can be improved significantlyif writers create documents with MT in mind. Thisarticle deals with ``MTranslatability' – translatabilityof texts by MT systems. It identifies characteristics oftext that decrease MTranslatability and suggests waysto improve them. It also illustrates the effect of writingfor MTranslatability by showing before-and-after picturesof output from various commercially available MT systems,and gives an overview of tools that help identify and correctthe problems. 相似文献
73.
Chopsticks are one of the most simple and popular hand tools ever invented by humans, but have not previously been investigated by ergonomists. Two laboratory studies were conducted in this research, using a randomised complete block design, to evaluate the effects of the length of the chopsticks on the food-serving performance of adults and children. Thirty-one male junior college students and 21 primary school pupils served as subjects for the experiment. The results showed that the food-pinching performance was significantly affected by the length of the chopsticks, and that chopsticks of about 240 and 180 mm long were optimal for adults and pupils, respectively. Based on these findings, the researchers suggested that families with children should provide both 240 and 180 mm long chopsticks. In addition, restaurants could provide 210 mm long chopsticks, considering the trade-offs between ergonomics and cost. 相似文献
74.
In recent years, educators and students are increasingly employing online collaboration applications such as Google Docs™ and PBWorks™ for group projects and assignments. Yet, the effectiveness of these emerging technologies has not been rigorously examined. Anchoring upon and informed by the existing literature, two design characteristics – sociability and visibility, and two human characteristics – gender and age, are focused on, which are salient in online collaboration applications. A field experiment was conducted to examine the direct and moderating effects of design and human characteristics on learning outcomes. The research found that sociability improved process satisfaction and positive social environment while visibility enhanced academic performance and solution satisfaction of learners. Males had higher solution satisfaction while older learners had higher academic performance. Moderating effects were also found. Both theoretical and practical implications are drawn. In particular, a rubric for online collaboration application selection for academic performance is conceived. This study provides empirical support for online collaboration application effectiveness in education which will augur well for future adoption, use and evolution. 相似文献
75.
《Ergonomics》2012,55(5):557-577
By their very nature laboratory experiments are at best only rough and approximate models of any real-life situation. First of all the possible independent variables that influence behaviour in any practical situation, a laboratory experiment selects only a. few for test. As a result, hidden or unsuspected interactions in real-life may easily nullify, or even reverse, conclusions arrived at in the laboratory. Second, variables always change when they are brought into the laboratory. Third, the effect of controlling extraneous or irrelevant variables in the laboratory is to increase the precision of an experiment but at the risk of discovering effects so small that they are of no practical importance. Fourth, the dependent variables (or criteria) used in laboratory experiments are variables of convenience. Rarely are they selected for their relevance to some practical situation. Last, the methods used to present variables in the laboratory are sometimes artificial and unrealistic. The safest and most honest conclusion to draw from all these considerations is that one should generalize with extreme caution from the results of laboratory experiments to the solution of practical problems. 相似文献
76.
The quality of the micro-mechanical machining outcome depends significantly on the tracking performance of the miniaturized
linear motor drive precision stage. The tracking behavior of a direct drive design is prone to uncertainties such as model
parameter variations and disturbances. Robust optimal tracking controller design for this kind of precision stages with mass
and damping ratio uncertainties was researched. The mass and damping ratio uncertainties were modeled as the structured parametric
uncertainty model. An identification method for obtaining the parametric uncertainties was developed by using unbiased least
square technique. The instantaneous frequency bandwidth of the external disturbance signals was analyzed by using short time
Fourier transform technique. A two loop tracking control strategy that combines the μ-synthesis and the disturbance observer
(DOB) techniques was proposed. The μ-synthesis technique was used to design robust optimal controllers based on structured
uncertainty models. By complementing the μ controller, the DOB was applied to further improving the disturbance rejection
performance. To evaluate the positioning performance of the proposed control strategy, the comparative experiments were conducted
on a prototype micro milling machine among four control schemes: the proposed two-loop tracking control, the single loop μ
control, the PID control and the PID with DOB control. The disturbance rejection performances, the root mean square (RMS)
tracking errors and the performance robustness of different control schemes were studied. The results reveal that the proposed
control scheme has the best positioning performance. It reduces the maximal errors caused by disturbance forces such as friction
force by 60% and the RMS errors by 63.4% compared with the PID control. Compared to PID with DOB control, it reduces the RMS
errors by 29.6%. 相似文献
77.
在机床热误差补偿技术研究中,热误差鲁棒建模是机床热误差补偿的成功关键之一。对国内外几种主要的热误差建模方法进行了较为深入的分析研究,比较了不同方法各自的优缺点,并针对缺点介绍了一些改进方法。在此基础上,总结归纳了目前研究存在的问题,并对未来的发展方向进行了探讨。 相似文献
78.
Three-dimensional molecular dynamics(MD)simulation was carried out to understand the mechanism of water lubrication in nanometric cutting.The water-lubricated cutting was compared with the dry cutting process in terms of lattice deformation,cutting force,heat and pressure distribution,and machined surface integrity.It was found that water molecules effectively reduce the friction between the tool and workpiece,the heat in the cutting zone and the pressure being generated on the tool surface,thus leading to prolonged tool life.Water molecules also enlarged the pressure-affected area,which decreased the roughness of the machined surface. 相似文献
79.
80.
1 Introduction With the forming of the global integrated environment ,the market competition of machine tools will be-come more intensely. At present ,the technology of the domestic machine tools is still behind relatively. Withregard to the designing method, we are still at the designing phase of experience ,static state and analogy. Weseldomthink of the structural dynamic characteristic ,andseldomuse the advanced designingtechnique and opti-mization software .Sothe quality and productioneff… 相似文献