Types of Facts

Additive:

Additive facts are facts that can be summed up through all of the dimensions in the fact table. A sales fact is a good example for additive fact.

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.

Eg: Daily balances fact can be summed up through the customers dimension but not through the time dimension.

Eg: Facts which have percentages, ratios calculated.

Non-Additive:

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

Factless Fact Table:

In the real world, it is possible to have a fact table that contains no measures or facts. These tables are called “Factless Fact tables”.

Eg: A fact table which has only product key and date key is a factless fact. There are no measures in this table. But still you can get the number products sold over a period of time.

Based on the above classifications, fact tables are categorized into two:

Cumulative:

This type of fact table describes what has happened over a period of time. For example, this fact table may describe the total sales by product by store by day. The facts for this type of fact tables are mostly additive facts. The first example presented here is a cumulative fact table.

Snapshot:

This type of fact table describes the state of things in a particular instance of time, and usually includes more semi-additive and non-additive facts. The second example presented here is a snapshot fact table.

Fact Table features

1. It provides measurement of an enterprise.

2. Measurement is the amount determined by observation.

3. Structure of Fact Table - foreign key (fk), Degenerated Dimension and Measurements.

4. Size of Fact Table is larger than Dimension Table.

5. In a schema less number of Fact Tables observed compared to Dimension Tables.

6. Compose of Degenerate Dimension fields act as Primary Key.

7. Values of the fields always in numeric or integer form.