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Sunday, March 16, 2008

STAR SCHEMA



Star Schema Modelling


A Dimensional modelling technique in which a detail fact table is linked to dimension tables. The data in data warehouses and data marts is accessed by end-users.

The information contained in the data warehouse/data mart must be easy for the end-user to use and access. Denormalized designs are easier for end-users to use than highly normalized designs, however these designs are more difficult to design and maintain.


The Star Schema diagram graphically models the end-user's view (i.e., the denormalized view) of how the information is accessed.



Components of a Star Schema Diagram


The diagram has three main components:



· Fact Table and its contents: metric attributes and the foreign keys necessary to join to the dimension tables,


· Dimension Tables and their contents: reference attributes, hierarchical attributes, and metric attributes. The dimension tables are highly denormalized,


· The lines that link the Dimension Tables to the Fact Table.


Star Schema Model

This diagram is a model of a star schema diagram.










Star Schema Example

The following is an example of a star schema for sales items.










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