转：http://searchdatamanagement.techtarget.com/definition/sparsity-and-density
查了一下定义，以免会写错
Sparsity and density are terms used to describe the percentage of cells in a database table that are not populated and populated, respectively. The sum of the sparsity and density should equal 100%.
A table that is 10% dense has 10% of its cells populated with non-zero values. It is therefore 90% sparse – meaning that 90% of its cells are either not filled with data or are zeros.
Because a processor adds up the zeros, sparcity can negatively impact processing time. In amultidimensional database sparsity can be avoided by linking cubes. Instead of creating a sparse cube for data that is not fully available, a separate but linked cube will ensure the data in the cubes remains consistent without slowing down processing.