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Dimensional Model
- A specific discipline for modeling data that is an alternative to Entity-Relationship (ER) model.
- Main components are Fact tables and Dimension tables.
- Better for decision support that an ER Model.
Dimensions
- Dimensions refer to Business Entities like Products, Airplanes, Type of Room, Person, House, etc.
- It is derived from the normalization of a single table.
- The most consistent dimension is the Date dimension.
Facts
- A Fact table stores observations/events such as Sales, Orders, Bookings, Flights, etc.
- A Fact is a measure that can be aggregated (finding the summary, average, median, min, max, count, etc.)
Important Terminology by Kimball and Ross (2013)
Grain:
- Each row in a Fact table is related with a measurement event.
- The data on each row is at a specific level of detail is the grain
Example:
One row per customer sold on a flight sales transaction
The most important:
Maintain the same grain throughout the rows of a Fact table.
