A "Star-Schema" model is comprised of a fact table and a number of dimension tables.
The fact table is a table with a multi-part key. Each element of the key is, itself a foreign key, to a single dimension table. The remaining fields in the fact table are known as facts, and are numeric, continuously valued, and additive. Facts can be thought of as measurements taken at the intersection of all of the dimensions.
Dimension attributes are mostly textual, and are almost always the source of constraints and report breaks.
This model enhances performance on known queries, or in other words, queries users run repeatedly day after day.
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