Page 197 - DCAP603_DATAWARE_HOUSING_AND_DATAMINING

Unit 10: Multi-dimensional Data Models and Aggregation

notes
figure 10.4: star schema

Dimension tables

A star schema stores all of the information about a dimension in a single table. Each level of a
hierarchy is represented by a column or column set in the dimension table. A dimension object
can be used to define the hierarchical relationship between two columns (or column sets) that
represent two levels of a hierarchy; without a dimension object, the hierarchical relationships are
defined only in metadata. Attributes are stored in columns of the dimension tables.
A snowflake schema normalises the dimension members by storing each level in a separate
table.

fact tables

Measures are stored in fact tables. Fact tables contain a composite primary key, which is composed
of several foreign keys (one for each dimension table) and a column for each measure that uses
these dimensions.

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