Types of FACT table

• Transactional FACT

• used to records one row per transaction with measures of particular business event.
• must be design with Additive facts
• takes more memory space in the database
• Contains additive Measures
• e.g
• 

• Periodic FACT

• used to records one row for a group of transactions with aggregated measures of business events that happen over a period of time.
• takes minimum memory space in the database when compare with Transaction fact table
• e.g.
• 

• Accumulating FACT

• used to records one row for the entire lifetime of transaction with measures of business events that happen over a period of time.
• must be design with combination of Additive facts with multiple date keys that helps to track the lifetime of business event
• takes minimum memory space in the database
• e.g.
• 

• Factless FACT

• A fact which does not contain any measure, called factless fact
• Used to maintain the mapping of different dimension keys
• e.g. in School database, we need to have a mapping which teacher is teaching which student, so when we create a table StudentTeacherMap, it will have just StudentKey and TeacherKey, so this table becomes factless fact

• Coverage FACT

• Factless fact can answer only optimistic queries, but cannot answer negative one
• If we talk about above example, then Factless Fact does NOT tell which teacher is NOT teaching which student
• So to cover all these scenarios, we need to introduce a flag in that table, which will have Y/N value based on their mapping and this becomes Coverage Fact