The document discusses concepts in the enhanced entity-relationship (EER) model including subclasses, superclasses, specialization, generalization, and attribute inheritance. It provides examples of how EMPLOYEE could have subclasses like SECRETARY, ENGINEER, etc. and how specialization is used to construct subclasses based on characteristics like job type or payment method. Generalization combines entity sets that share features into a higher-level set, and specialization and generalization can be represented in EER diagrams along with constraints like disjointness and completeness.

1. Enhanced-ER (EER) Model Concepts ♦ The EER model introduce the additional concepts of subclasses, superclasses, specialization generalization, attribute inheritance. The resulting model is called the enhanced-ER or Extended ER model. It is used to model applications more completely and accurately if needed. It includes some object-oriented concepts, such as inheritance . 14

3. Example: EMPLOYEE may be further grouped into SECRETARY, ENGINEER, MANAGER, TECHNICIAN, SALARIED_EMPLOYEE, HOURLY_EMPLOYEE,…

4. Each of these groupings is a subset of EMPLOYEE entities

5. Each is called a subclass of EMPLOYEE

6. EMPLOYEE is the superclass for each of these subclasses 14

8. Example: EMPLOYEE/SECRETARY, EMPLOYEE/TECHNICIAN

9. These are also called IS-A relationships (SECRETARY IS-A EMPLOYEE, TECHNICIAN IS-A EMPLOYEE, …).

10. To show class/subclass relationships, useU 14

11. Subclasses and Superclasses 14

13. It also inherits all relationships 14

15. Is the process of defining a set of subclasses of a superclass

16. The set of subclasses is based upon some distinguishing characteristics of the entities in the superclass

17. Example: {SECRETARY, ENGINEER, TECHNICIAN} is a specialization of EMPLOYEE based upon job type.

18. May have several specializations of the same superclass 14

20. Superclass/subclass relationships and specialization can be diagrammatically represented in EER diagrams

21. Attributes of a subclass are called specific attributes. For example, TypingSpeed of SECRETARY14

22. Example of Specialization 14

24. A bottom-up design process – combine a number of entity sets that share the same features into a higher-level entity set.14

26. Several classes with common features are generalized into a superclass; original classes become its subclasses

27. Example: CAR, TRUCK generalized into VEHICLE; both CAR, TRUCK become subclasses of the superclass VEHICLE.

28. We can view {CAR, TRUCK} as a specialization of VEHICLE

29. Alternatively, we can view VEHICLE as a generalization of CAR and TRUCK 14

30. GENERALIZATION AND SPECIALIZATION sid student name is A Specialization Generalization graduate Undergrad 14

32. Specifies that the subclasses of the specialization must be disjointed (an entity can be a member of at most one of the subclasses of the specialization)

33. Specified by d in EER diagram

34. If not disjointed, overlap; that is the same entity may be a member of more than one subclass of the specialization

35. Specified by o in EER diagram 14

37. Total specifies that every entity in the superclass must be a member of some subclass in the specialization/ generalization

38. Shown in EER diagrams by a double line

39. Partial specialization – each entity of a superclass does not have to belong to some subclass of a specialization

40. Shown in EER diagrams by a single line14

41. Constraints and example 14