IAB201 Lecture Notes - Lecture 5: Subtyping, Fact Table, Tuple
Document Summary
Step 5 - add mandatory role constraints, and check for logical derivations. In step 5 of the cdsp, each role is classified as mandatory or optional. 8853020: we record each patient"s name, but it is optional whether we record a phone number, the question mark "?" denotes a null, indicating that an actual value is not recorded. Mandatory role constraints: establishes a constraint where something must exist, paired with a uniqueness constraint it prevents any other entity types instances being introduced unless the mandatory role constraint is fulfilled. E. g. can"t have patient details until a patient name is in the system. "a mandatory role constraint is present on a role of an entity type if every instance of that entity type must be involved in that role. The information system understands the world as we specify it in the schema. It cannot enforce real world constraints not captured in the schema.
