There is INTEGRITY CONSTRAINTS on database.Types of integrity constraints are: (1) Non-null (2) Key (3) Referential integrity (4) Attribute-based (5) Tuple-based (6) General assertions Example schema: Student(ID, name, address, GPA, SAT) Campus(location, enrollment, rank) Apply(ID, location, date, major, decision) Example constraints:- A student with GPA 3.0 can only apply to campuses with rank 4.- All applications with date 1/1/01 have non-NULL decision.- Apply.ID and Apply.location appear in Student.ID and Campus.location, respectively.- Campus.rank 10.
Constraints are rules applied to a theme. The Scenario evaluates the features ofthe theme based on the rule and informs the user when a feature or features breaksit. A typical Constraint would be that buildings can only be constructed on slopesless than a certain value. If, in the course of laying out a new subdivision, theuser places a building on a steep slope, then Scenario Constructor will display awarning. The user can heed the warning and change the position of the building orleave it where it is. Constraints do not have to be followed.