1. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban1 ADVANCED DATABASE CONCEPTS Enhanced Entity Relationship Modeling Susan D. Urban and Suzanne W. Dietrich Department of Computer Science and Engineering Arizona State University Tempe, AZ 85287-5406

2. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban2 OUTLINE Enhanced Entity-Relationship model (EER). Generalization and Specialization Categories Summary of Constraints Captured.

3. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban3 THE ON-LINE SHOPPING ER SCHEMA

4. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban4 THE ENHANCED ENTITY-RELATIONSHIP (EER) MODEL An entity definition is known as a class. –A specific occurrence of an entity is an instance of a class. Classes can be formed into superclass/subclass hierarchies using generalization and specialization. –The ISA relationship. –Inheritance of attributes. –Constraints on subclass membership. Categories are used to represent a union of classes. The EER model extends the ER model with advanced modeling features:

5. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban5 GENERALIZATION vs. SPECIALIZATION Generalization is the process of viewing several different objects in a higher level, abstract form. –Generalization suppresses the differences between objects and emphasizes the similarities. Specialization is the process of viewing an object as a more refined, specialized object. –Specialization is the opposite of generalization. –Specialization emphasizes the differences between objects.

6. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban6 GENERALIZATION AND SPECIALIZATION IN THE EER MODEL

7. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban7 INHERITANCE An instance of a subclass is an instance of its superclass (also known as the ISA relationship). –A Celebrity ISA Person. Due to the ISA relationship, an instance of a subclass inherits attributes from it superclass. –A Celebrity inherits ssn, name, phone, gender, and address from Person. –A Model inherits birthDate from Celebrity. The inheritance of attributes is a transitive relationship. –If a Model ISA Celebrity and a Celebrity ISA Person, then a Model inherits ssn, name, phone, gender, and address from Person.

8. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban8 CONSTRAINTS ON SPECIALIZATION Disjoint Constraint If the disjoint constraint is specified, the instances of the subclasses of a specialization must be disjoint. If the disjoint constraint is not specified, then the instances of subclasses can be overlapping.

9. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban9 CONSTRAINTS ON SPECIALIZATION Completeness Constraint Total specialization - Every instance of a superclass must be an instance of at least one of its subclasses (also known as a covering constraint). Partial specialization - An instance of a superclass is not required to be an instance of any of its subclasses.

10. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban10 SPECIALIZATION USING DISJOINT AND COMPLETENESS CONSTRAINTS

11. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban11 CONSTRAINTS ON SUBCLASS MEMBERSHIP A specialization can be: Attribute-defined - Determines membership in a subclass by placing a condition on the value of an attribute in the superclass. User-defined - Membership in a subclass does not depend on any specific attribute value. Membership is determined by the user.

12. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban12 ATTRIBUTE-DEFINED SPECIALIZATION

13. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban13 USER-DEFINED SPECIALIZATION

14. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban14 MULTIPLE SPECIALIZATIONS OF A CLASS Attribute and User-Defined Specializations

15. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban15 RULES FOR USE OF ATTRIBUTE-DEFINED SUBCLASSES If the specialization attribute at the superclass level is single- valued, membership at the subclass level is always disjoint. If the specialization attribute at the superclass level is multi- valued, membership at the subclass level is always overlapping. If the specialization is total, the attribute value in the superclass is required. If the specialization is partial, the specialization attribute value in the superclass is optional. The presence of a value, however, implies automatic insertion at the subclass level.

16. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban16 RULES FOR USE OF SUPERCLASS/SUBCLASS HIERARCHIES Deleting an entity from a superclass implies automatic deletion of the entity from all subclasses. Deleting an entity from a subclass does not imply deleting the entity from its superclass. However, attributed-defined constraints must not be violated. At the superclass level, changing the value of an attribute used for attribute-defined specialization requires appropriate changes in subclass membership.

17. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban17 MULTIPLE INHERITANCE In a specialization hierarchy, every subclass has only one superclass. In a specialization lattice, a subclass can have more than one superclass. –The subclass is referred to as a shared subclass. –A specialization lattice demonstrates multiple inheritance. –A shared subclass must satisfy the multiple inheritance intersection constraint, where each instance of the shared subclass is an instance of all of its superclasses.

18. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban18 MULTIPLE INHERITANCE StarModel = MovieStar  Model

19. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban19 SUMMARY OF EER HIERARCHY CONSTRAINTS ISA Constraint - an instance of a subclass must be an instance of its superclass. Disjoint Constraint: Disjoint vs. Overlapping subclass membership. Completeness Constraint: Total vs. Partial specialization at the subclass level. Attribute-Defined Constraint: The value of an attribute at the superclass level determines automatic membership of the instance at the subclass level. Multiple Inheritance Intersection Constraint - The instances of a shared subclass must represent the intersection of its superclasses.

20. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban20 CATEGORIES AND CATEGORIZATION If a subclass can be traced to more than one base superclass, then the subclass is called a category. A category represents a union of its superclasses, where an instance of a category subclass must be an instance of at least one superclass, but is not necessarily a member of all superclasses.

21. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban21 CONSTRAINTS ON CATEGORIZATION Total categorization - Every instance of a superclass must be an instance of the category. Partial categorization - An instance of a superclass is not required to be an instance of the category. C = A  B F  (D  E)

22. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban22 CATEGORIES AND CATEGORIZATION Partial Categorization of Sponsor

23. Enhanced Entity Relationship Modeling © 2002 by Dietrich and Urban23 HOLLYWOOD DATABASE SCHEMA