We know that fact table is a collection of many facts and measures having multiple keys joined with one or more dimesion tables.Facts contain both numeric and additive fields.But factless fact table are different from all these.
A factless fact table is fact table that does not contain fact.They contain only dimesional keys and it captures events that happen only at information level but not included in the calculations level.just an information about an event that happen over a period.
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:
Tracking student attendance or registration events
Tracking insurance-related accident events
Identifying building, facility, and equipment schedules for a hospital or university
Factless fact tables are used for tracking a process or collecting stats. They are called so because, the fact table does not have aggregatable numeric values or information.There are two types of factless fact tables: those that describe events, and those that describe conditions. Both may play important roles in your dimensional models.
Factless fact tables for Events
The first type of factless fact table is a table that records an event. Many event-tracking tables in dimensional data warehouses turn out to be factless.Sometimes there seem to be no facts associated with an important business process. Events or activities occur that you wish to track, but you find no measurements. In situations like this, build a standard transaction-grained fact table that contains no facts