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. For example:
Current_Balance and Profit_Margin are the facts. Current_Balance is a semi-additive
fact, as it makes sense to add them up for all accounts (what’s the total current
balance for all accounts in the bank?), but it does not make sense to add them up
through time (adding up all current balances for a given account for each day of the
month does not give us any useful information 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.