在ISO 9421里提到，某一事物的可用性应当可以以效力(effectiveness)、效率(efficiency)和满意度(satisfaction)三个维度来进行衡量。
ISO 9421 says that the usability of something should be measured in terms of it's effectiveness, efficiency and satisfaction.
直接建立维度表与事实表的位图连接索引会产生大量无用的索引项，影响查询效率。
Building bitmap join indexes of dimension tables and fact tables directly may bring a large number of useless index items that affect query efficiency.
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