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Slide 1: 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 Enhanced Entity Relationship Modeling 1 © 2002 by Dietrich and Urban
Slide 2: OUTLINE • Review of Entity-Relationship model (ER). • Enhanced Entity-Relationship model (EER). • Generalization and Specialization • Categories • Summary of Constraints Captured. Enhanced Entity Relationship Modeling 2 © 2002 by Dietrich and Urban
Slide 3: ENTITY RELATIONSHIP (ER) MODEL Enhanced Entity Relationship Modeling 3 © 2002 by Dietrich and Urban
Slide 4: CARDINALITIES FOR N-ARY RELATIONSHIP A Car is related to only 1 (Person, Bank) pair. A Person is related to M (Car, Bank) pairs. A Bank is related to N (Car, Person) pairs. Enhanced Entity Relationship Modeling 4 © 2002 by Dietrich and Urban
Slide 5: ALTERNATIVE FOR N-ARY RELATIONSHIP Enhanced Entity Relationship Modeling 5 © 2002 by Dietrich and Urban
Slide 6: ER MODEL WITH (MIN, MAX) PAIRS Enhanced Entity Relationship Modeling 6 © 2002 by Dietrich and Urban
Slide 7: SUMMARY OF ER MODELING CONSTRAINTS • Classes Key Constraint – Unique identification of entities. • Structural Constraints on Relationships Cardinality Constraints: 1:1, 1:N, M:N Participation Constraints: Total vs. Partial (Min..Max) Constraints: Min = 0 (Partial Participation) Min >=1 (Total Participation) Max = n, (An upper bound on relationship participation) Enhanced Entity Relationship Modeling 7 © 2002 by Dietrich and Urban
Slide 8: THE ON-LINE SHOPPING ER SCHEMA Enhanced Entity Relationship Modeling 8 © 2002 by Dietrich and Urban
Slide 9: THE ENHANCED ENTITY-RELATIONSHIP (EER) MODEL The EER model extends the ER model with advanced modeling features: • 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. Enhanced Entity Relationship Modeling 9 © 2002 by Dietrich and Urban
Slide 10: 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. Enhanced Entity Relationship Modeling 10 © 2002 by Dietrich and Urban
Slide 11: GENERALIZATION AND SPECIALIZATION IN THE EER MODEL Enhanced Entity Relationship Modeling 11 © 2002 by Dietrich and Urban
Slide 12: 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. Enhanced Entity Relationship Modeling 12 © 2002 by Dietrich and Urban
Slide 13: 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. Enhanced Entity Relationship Modeling 13 © 2002 by Dietrich and Urban
Slide 14: 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. Enhanced Entity Relationship Modeling 14 © 2002 by Dietrich and Urban
Slide 15: SPECIALIZATION USING DISJOINT AND COMPLETENESS CONSTRAINTS Enhanced Entity Relationship Modeling 15 © 2002 by Dietrich and Urban
Slide 16: 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. Enhanced Entity Relationship Modeling 16 © 2002 by Dietrich and Urban
Slide 17: ATTRIBUTE-DEFINED SPECIALIZATION Enhanced Entity Relationship Modeling 17 © 2002 by Dietrich and Urban
Slide 18: USER-DEFINED SPECIALIZATION Enhanced Entity Relationship Modeling 18 © 2002 by Dietrich and Urban
Slide 19: MULTIPLE SPECIALIZATIONS OF A CLASS Attribute and User-Defined Specializations Enhanced Entity Relationship Modeling 19 © 2002 by Dietrich and Urban
Slide 20: RULES FOR USE OF ATTRIBUTE-DEFINED SUBCLASSES • If the specialization attribute at the superclass level is singlevalued, membership at the subclass level is always disjoint. • If the specialization attribute at the superclass level is multivalued, 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. Enhanced Entity Relationship Modeling 20 © 2002 by Dietrich and Urban
Slide 21: 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. Enhanced Entity Relationship Modeling 21 © 2002 by Dietrich and Urban
Slide 22: 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. Enhanced Entity Relationship Modeling 22 © 2002 by Dietrich and Urban
Slide 23: MULTIPLE INHERITANCE StarModel = MovieStar  Model Enhanced Entity Relationship Modeling 23 © 2002 by Dietrich and Urban
Slide 24: 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. Enhanced Entity Relationship Modeling 24 © 2002 by Dietrich and Urban
Slide 25: 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. Enhanced Entity Relationship Modeling 25 © 2002 by Dietrich and Urban
Slide 26: 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 Enhanced Entity Relationship Modeling 26 F  (D  E) © 2002 by Dietrich and Urban
Slide 27: CATEGORIES AND CATEGORIZATION Partial Categorization of Sponsor Enhanced Entity Relationship Modeling 27 © 2002 by Dietrich and Urban
Slide 28: HOLLYWOOD DATABASE SCHEMA Enhanced Entity Relationship Modeling 28 © 2002 by Dietrich and Urban