Question

1. Explain the following IN YOUR OWN WORDS (Not interested in textbook/slide definition):

1. Supertype
2. Subtype
3. Disjointness Constraint
4. Overlap Rule
5. Generalization with respect to supertype and subtype
6. Specialization with respect to supertype and subtype
7. Inheritance with respect to supertype and subtype

Answer 1

Solving The First 4 Parts

Answer a) Super type is used in Data Modelling in which an entity type with only common attributes are described for many entity subtypes that use this supertype.

Answer b) Subtypes are entered into the model to reduce the total number of attributes of each entity. Each entity wll have unique attributes to reduce duplication. Subtypes also reduce the problem of large databases so that data with similar attributes can be grouped together.

Example to further explain Supertype and Subtype:

If we are to create a database of employees working in a hotel. We put them into 3 types of departments:

Administration

Housekeeping

Restaurant

Here , the supertype will be employees and subtype will be Administration, Housekeeping and Restaurant. Please note that subtype will reduce the problem of having large databases.

Answer c) Disjointness constraint means that subtypes do not have common entities i.e. intersection between subtypes is empty.

Answer d) Overlap rule indicates that a supertype instance may be a member of two or more subtypes.

Example: In the previous database, en employee (supertype instance) might be working in both Housekeeping and Administration subtypes.