Enhanced Entity-Relationship and Object Modeling

1. 4-1 Chapter 4 Enhanced Entity-Relationship and Object Modeling

2. 4-2 database applications traditional database processing applications in business and industry newer applications CAD/CAM telecommunications images and graphics multimedia data mining data warehousing GIS databases for indexing the World Wide Web ...

3. 4-3 Enhanced ER (EER) model modeling concepts of the ER model subclass and superclass (type inheritance) specialization and generalization (constraints) category (UNION) attribute and relationship inheritance UNIVERSITY database in EER model

4. 4-4 subclass entity type (a type of entity) e.g., EMPLOYEE entity set (collection of entities of that type) e.g., current set of EMPLOYEE entities subclass (vs superclass) e.g., SECRETARY, ENGINEER, TECHNICIAN, MANAGER, SALARIED_EMPLOYEE, HOURLY_EMPLOYEE class/subclass relationship e.g., EMPLOYEE/SECRETARY

5. 4-5 subclass (continued) Implementation A member entity of the subclass represents the same real-world entity as some member of the superclass the same entity but in specific role A distinct record that is related via the key attribute to its superclass entity type inheritance Besides specific (or local) attributes  and relationships, An entity that is a member of a subclass inherits all the attributes of the entity as a member of the superclass The entity also inherits all the relationships in which the superclass participates

6. 4-6 Specialization and Generalization specialization define a set of subclasses of an entity type {SECRETARY, ENGINEER, TECHNICIAN} is a specialization of EMPLOYEE by job type {SALARIED_EMPLOYEE, HOURLY_EMPLOYEE} is a specialization of EMPLOYEE by method of pay notation in EER diagram

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9. 4-9 Why including class/subclass relationships? Certain attributes may apply to some but not all entities of the superclass SECRETARY (attribute TypingSpeed) ENGINEER (attribute EngineerType) Some relationship types may be participated in only by entities that are members of the subclass HOURLY_EMPLOYEE belongs to a trade union

10. 4-10 Specialization process Define a set of subclasses of an entity type Establish additional specific attributes with each class Establish additional specific relationship types between subclass and other entity types or other subclasses

11. 4-11 Generalization Define a generalized entity type from the given entity types {CAR, TRUCK} as a specialization of VEHICLE VEHICLE as a generalization of CAR and TRUCK

12. 4-12

13. 4-13 Constraints onSpecialization and Generalization single subclass only {MANAGER} specification predicate-defined subclasses determined by a condition (JobType = �Secretary�) <--- defining predicate attribute-defined specialization (see Figure 4.4 at 4-14) membership condition on the same attribute of the superclass (defining attribute) user-defined subclass determined by the database users {HOURLY_EMPLOYEE, SALARIED_EMPLOYEE}

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15. 4-15 Constraints (continued) disjointness constraint an entity can be a member of at most one of the subclasses of the specialization attribute-defined specialization --> defining attribute is singled-valued d : disjoint for attribute/user-defined subclass o : an entity may be a member of more than one subclass of a specialization

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17. 4-17 Constraints (continued) completeness constraint (4-7) total specialization constraint every entity in the superclass must be a member of some subclass in the specialization e.g., {HOURLY_EMPLOYEE, SALARIED_EMPLOYEE} notation: superclass partial specialization constraint an entity may not belong to any of the subclasses e.g., {SECRETARY, ENGINEER, TECHNICIAN}

18. 4-18 Constraints (continued) disjointness and completeness constraints are independent Disjoint, total Disjoint, partial Overlapping, total Overlapping, partial a superclass identified through generalization process usually is total

19. 4-19 Some insertion/deletion rules for specialization/generalization Deleting an entity from a superclass it is automatically deleted from all the subclasses to which it belongs Inserting an entity in a superclass it is mandatorily inserted in all predicate-defined (or attribute-defined) subclasses for which it satisfies the defining predicate Inserting an entity in a superclass of a total specialization it is mandatorily inserted in at lease one of subclasses

20. 4-20 Specialization/Generalization Hierarchies and Lattices A subclass itself may have further subclasses specified on it. Specialization hierarchy every subclass participates as a subclass in only one class/subclass relationship Specialization lattice a subclass can be a subclass in more than one class/subclass relationship

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23. 4-23 Specialization/Generalizationin Conceptual Data Modeling top-down conceptual refinement process a specialization process bottom-up conceptual synthesis a generalization process combination

24. 4-24 union type (or category) a single superclass vs. more than one superclass ENGINEERING_MANAGER is a subclass in three distinct superclass/subclass relationship (4-21) Each has single superclass union type or category model a single superclass/subclass relationship with more than one superclass the subclass represents a collection of objects that is (a subset of) the UNION of distinct entity types e.g., OWNER is a subclass of the UNION of (COMPANY, BANK, PERSON)

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26. 4-26 category vs. shared subclass intersection shared subclass (Fig. 4.6, 4-21) ENGINEERING_MANAGER is a subset of the intersection of ENGINEER, MANAGER, and SALARIED_EMPLOYEE an engineering manager must be an ENGINEER, a MANAGER, and a SALARIED_EMPLOYEE ENGINEERING_MANAGER inherits all the attributes of its superclasses union category (Fig. 4.8, 4-25) OWNER is a subset of the union of COMPANY, a BANK, or a person an OWNER may be a COMPANY, a BANK, or a PERSON an OWNER entity inherits the attributes depending on the superclass to which the entity belongs

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28. 4-28 An Example UNIVERSITYEER Schema

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30. 4-30 Formal Definitions class a set or collection of entities, including any of the EER schema constructs that group entities such as entity types, subclasses, superclasses, and categories subclass S a class whose entities must always be a subset of the entities in another class C (superclass) of the superclass/subclass relationship C/S S ? C

31. 4-31 Formal Definitions(continued) specialization Z = {S1, S2, �, Sn) a set of subclasses that have the same superclass G G/Si is a superclass/subclass relationship  generalization total partial (otherwise) disjoint overlapping (otherwise) predicate-defined user-defined (otherwise) a predicate p on the attributes of G is used to specify which entries in G are members of S

32. 4-32 Formal Definitions(continued) specialization Z (generalization G) is attribute-defined a predicate (A=ci) is used to specify membership in each subclass Si in Z category T a class that is a subset of the union of n defining superclasses D1, D2, �, Dn T ? (D1 ? D2 ? � ? Dn) relationship type: allow class to participate in a relationship

33. 4-33 Conceptual Object Modeling Using UML Class Diagrams UML - Universal Modeling Language OMT - Object Modeling Technique

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35. 4-33.2 4-35

36. 4-34 4-36 Relationships of Higher Degree Relationship types of degree 2 are called binary Relationship types of degree 3 are called ternary and of degree n are called n-ary In general, an n-ary relationship is not equivalent to n-binary relationships

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38. 4-36 4-38