Homework SourseHow can I distinguish between condition defined constraint a
How can I distinguish between condition defined constraint and user defined constraint?
How can I distinguish between condition defined constraint and user defined constraint?
Solution
CONDITION DEFINED
USER DEFINED
Membership is evaluated on the basis of whether or not an entity satisfies an explicit condition or predicate.
Database user assigns entities to a given entity set
| CONDITION DEFINED | USER DEFINED | |
| Membership is evaluated on the basis of whether or not an entity satisfies an explicit condition or predicate. | Database user assigns entities to a given entity set | |
| In a generalization – specialization hierarchy, it must be possible to decide which entities are members of which lower level entity sets. In a condition defined design constraint, membership in the lower level entity-sets is evaluated on the basis of whether or not an entity satisfies an explicit condition or predicate | User-defined lower-level entity sets are not constrained by a membership condition; rather, entities are assigned to a given entity set by the database user. | |
| Condition-defined constraints alone can be automatically handled by the system |
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| Whenever any tuple is inserted into the database, its membership in the various lower level entity-sets can be automatically decided by evaluating the respective membership predicates. Similarly when a tuple is updated, its membership in the various entity sets can be re-evaluated automatically. | Membership is decided by user.It is not automatic. |
