Step-3: A Fact-less Fact Table

• “Fact-less” fact table
  • A fact table without numeric fact columns

• Captures relationships between dimensions

• Use a dummy fact column that always has value 1

The problem of not recording non-events is solved by using fact-less fact tables, as not recording such information resulted in loss of data. Such a fact-less fact table is one which does not have numeric values stored in the corresponding column, as such tables are used to capture the relationships between dimensions. Fact less fact table captures the many-to-many relationships between dimensions, but contains no numeric or textual facts. To achieve this dummy value of 1 is used in the corresponding column.

Example: Fact-less Fact Tables

Examples:

• Department/Student mapping fact table

• What is the major for each student?

• Which students did not enroll in ANY course

• Promotion coverage fact table

• Which products were on promotion in which stores for which days?

• Kind of like a periodic snapshot fact

Some of the examples of fact-less fact tables. Consider the case of a department/student mapping fact table. The data is recorded for each student who registers for a course, but there may be students that do not register in any course. If data is useful from the point of view of identifying those students which are skipping a semester. There is no direct or simple way to identify such students, the solution is a fact-less fact table. Similarly which items on promotion are not selling, as the sales records are for only those items that are sold.

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