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In a Data Warehousing star schema, the data that defines what a particular dimension consist of is stored in one or more dimension tables. Columns within the dimension table(s) are grouped into levels. Information about levels is stored in the USER_DIM_LEVELS and related Data Dictionary views. These relate the level to both the dimension and the dimension table.

A good example is provided by Hora's display of the PROMOTIONS_DIM dimension in Oracle's SH sample schema. Here, the levels of PROMOTIONS_DIM are shown at the top of the tree view, with the table and column names below them. For level PROMO, PROMOTIONS.PROMO_ID is the level key, and the remaining columns are indented below it.



Levels are used to define hierarchies within a dimension.