Dimensions are of 3 types mainly in case of slowly changing dimensions:
Type 1 ->Doesnt maintain any history and is update only.
Type 2-> Maintains full history.Insert row when certain attributes change else update row.The latest record is identified by a flag or date field which is called the MRI or Most Recent Indicator
Type 3->Maintains partial history.History is maintained as columns and not rows.Hence it is predecided as to till how many levels of history you want to maintain.
There are three types of Dimesions
Confirmed Dimensios, Junk Dimesions, Degenerative Dimesions
Comfirmed is some thing which can be shared by shared by multiple Fact Tables or multiple Data Marts.
Junk Dimensiions is grouping flagged values
Degenerative Dimension is something dimensional in nature but exist fact table.
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