• Journal of KIISE:Databases
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• v.36 no.3
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• pp.226-234
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• 2009

A data stream is a massive unbounded sequence of data elements continuously generated at a rapid rate. Due to the characteristics of a data stream, it is impossible to save all the data elements of a data stream. Therefore it is necessary to define a new synopsis structure to store the summary information of a data stream. For this purpose, this paper proposes a cuboid prefix tree that can be effectively employed in evaluating an iceberg query over data streams. A cuboid prefix tree only stores those itemsets that consist of grouping attributes used in GROUP BY query. In addition, a cuboid prefix tree can compute multiple iceberg queries simultaneously by sharing their common sub-expressions. A cuboid prefix tree evaluates an iceberg query over an infinitely generated data stream while efficiently reducing memory usage and processing time, which is verified by a series of experiments.

• Education of Primary School Mathematics
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• v.14 no.3
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• pp.237-259
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• 2011

Mathematics learning disabilities is a specific learning disorder affecting the normal acquisition of arithmetic and spatial skills. Reported prevalence rates range from 5 to 10 percent and show high rates of comorbid disabilities, such as dyslexia and ADHD. In this study, the characteristics and the causes of this disorder has been examined. The core cause of mathematics learning disabilities is not clear yet: it can come from general cognitive problems, or disorder of innate intuitive number module could be the cause. Recently, researchers try to subdivide mathematics learning disabilities as (1) semantic/memory type, (2) procedural/skill type, (3) visuospatial type, and (4) reasoning type. Each subtype is related to specific brain areas subserving mathematical cognition. Based on these findings, the author has performed a basic research to develop grade specific diagnostic tests: number processing test and math word problems for lower grades and comprehensive math knowledge tests for the upper grades. The results should help teachers to find out prior knowledge, specific weaknesses of students, and plan personalized intervention program. The author suggest diagnostic tests are organized into 6 components. They are number sense, conceptual knowledge, arithmetic facts retrieval, procedural skills, mathematical reasoning/word problem solving, and visuospatial perception tests. This grouping will also help the examiner to figure out the processing time for each component.

• Archives of design research
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• v.20
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• pp.199-208
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• 1997

The emphasis of simplicity in design is because of the desire to deliver much content with a simplest way. Since in general, a simple form is outstanding in its symbolical nature and the relief of plastic beauty is easy by it, it is usually applied to a form of a symbol mark. However, in the meantime, if any local autonomous group or enterprise which has not tried to give efforts to its advertisement than they might expect and might be disadvantageous in competition. For consumers, when they experienced several, forms of simple, symbol mark, would not remember the special features of each mark. Rather, for the psychology of perception, they might remember only the formative, common features, there by grouping the marks by their common features. In this study, some symbol marks in Dobong-gu Ward Office and Wonju city were inspected, reviewed, and analized. And its is a finding that the subjects of this study could not distinguish or identify any of marks from another mark having a similar image of it: the reason is that the simplicity of a symbol mark made or allowed them to recognize it identical with the other imaged: it proves that the mistakes, defects of memory, and accumulated errors are oriented to the identical image. After all, the appearented image and perceived image are differnt. Any of symbolmarks which takes a simple form does not mean the perceived image is also simple. As a final conclusion, designers, in order to produce any of competitive symbolmarks, need to thoroughly understand psychology of gestalt.