度量維度(measures group)

在數(shù)據(jù)方中的一些概念如維度(Dimension),度量(Measure),度量組(measure group),層次(hierarchy),級(jí)別(level)是很容易理解的,有個(gè)概念 度量維度(measures group)讓人理解起來(lái)非常困難。
????????MSDN的解釋如下，"A measures dimension is the dimension that contains all of the measures in a cube. A measures dimension is a special type of dimension in which the members are typically aggregated (generally by sum or by count) based on the current member of each dimension attribute with which a specified measure exists"
??????? 仔細(xì)研究以后發(fā)現(xiàn)，其實(shí)此處的度量維度就是指所有的度量，換句話說(shuō)度量被當(dāng)成了一種特殊的維度，這個(gè)維度如果有層次結(jié)構(gòu)的話，他的層次結(jié)構(gòu)也只能有一個(gè)級(jí)別,只所以混淆是因?yàn)樗彩且环N維度,不過(guò)是特殊的維度。 http://www.cnblogs.com/anshangcun/archive/2007/10/30/943360.html 度量值組 度量值組?(Measure Group)“度量值組”是 SQL Server Analysis Services 中一個(gè)多維數(shù)據(jù)集的相關(guān)度量值集合（通常是來(lái)自同一事實(shí)數(shù)據(jù)表... ------------------- Measures and Measure Groups A measure represents a column that contains quantifiable data, usually numeric, that can be aggregated. A measure is generally mapped to a column in a fact table.?
? Attribute columns from dimension tables can be used to define measures, but such measures are typically semiadditive or nonadditive in terms of their aggregation behavior.?
? You can also define a measure as a calculated member by using a Multidimensional Expressions (MDX) to provide a calculated value for a measure based on other measures in the cube.?

Measure Groups
? In a cube, measures are grouped by their underlying fact tables into measure groups. Measure groups are used to associate dimensions with measures.?

? The fact table contains two basic types of columns: attribute columns and measure columns. Attribute columns are used to create foreign key relationships to dimension tables, so that the quantifiable data in the measure columns can be organized by the data contained in the dimension tables.Attribute columns are also used to define the granularity of a fact table and its measure group.

Granularity
? Granularity refers to the level of detail supported by a fact table.?
? The granularity of a measure group can never be set finer than the lowest level of the dimension from which the measure group is viewed, but the granularity can be made coarser by using additional attributes.?

Aggregate Functions
??When a dimension is used to organize measures in a measure group, the measure is summarized along the hierarchies contained in that dimension. The summation behavior depends on the aggregate function specified for the measure. http://www.cnblogs.com/csgashine/articles/559377.html

轉(zhuǎn)載于:https://www.cnblogs.com/taoyizhuoma/p/6009876.html

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