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INTRODUCTION The CUBE BY operator (Gray et al., 1996) is anessential facility for data warehousing and OLAP. Itis a multidimensional extension of the standardGROUP BY operator, computing all possible com-binations of the grouping attributes in the CUBE BYclause. A CUBE BY with N grouping attributes willcompute 2N group-bys. In the real world, a fact tableis often very large and sparse. In such cases, the sizeof a group-by is possibly close to the size of the facttable. So th… 相似文献
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Though many compression methods are based on the use of variable length codes, there has recently been a trend to search for alternatives in which the lengths of the codewords are more restricted, which can have useful applications, such as easier processing and fast decoding. This paper explores the construction of variable-to-fixed length codes, which have been suggested long ago by Tunstall. Using new heuristics based on suffix trees, the performance of Tunstall codes can in some cases be improved by more than 40%. 相似文献
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崔山佳 《宁波广播电视大学学报》2005,3(1):30-32,55
《金瓶梅词话》中带“儿”尾现象十分常见,尤其是动词重叠后“儿”尾现象更见特色。本文分析了十三种形式,有单音节的动词重叠,也有双音节的动词重叠,还有双音节和单音节结合的动词重叠,其中尤以单音节的数量为多,形式也多种多样,而且更具特点;动词重叠带“儿”尾的语法作用,与一般动词重叠的语法作用也有差别,即前者没有带宾语的,而后者带宾语常用。 相似文献
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装箱问题作为一种常见的运筹问题,在很多领域有着重要的应用,装箱问题可以分为一维、二维和三维装箱.主要讨论了二维装箱中条形装箱问题的遗传算法的求解,其中采用后缀表达式的形式对装箱方案进行编码,并详细提出了解码的算法和有关的证明,最后通过实例证明了该算法是可行的. 相似文献