Fact Table

Fact Table

• A Fact table is a collection of facts and foreign key relations to the dimensions.

               The central table in a star join schema, characterized by a composite key, each of whose elements is a foreign key drawn from a dimension table. Facts are information about the business, typically numeric and additive. A table that contains the measures that the business users wish to analyze to find new trends or to understand the success or failure of the organization.

Types

• Measures
• Conformed Facts

 Measures

Measure objects retrieve numeric data, or data that is the result of calculations on data in the database. Measure objects are semantically dynamic: the values they return depend on the objects they are used with

Types

Additive – Additive facts are facts that can be summed up for the dimensions present in the fact table.

Non-Additive - Non-additive facts are facts that cannot be summed up for any of the dimensions present in the fact table.

Semi-Additive - Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others.

Factless fact - A factless fact table captures the many-to-many relationships between

dimensions, but contains no numeric or textual facts. They are often used to record events or

coverage information.

Common examples of factless fact tables include:

• Identifying product promotion events (to determine promoted products that didn’t sell)
• Tracking student attendance or registration events
• Tracking insurance-related accident events
• Identifying building, facility, and equipment schedules for a hospital or university