1. © 2002 by Prentice Hall 1 David M. Kroenke Database Processing Eighth Edition Chapter 3 The Entity- Relationship Model

2. © 2002 by Prentice Hall 2 Data Modeling Process of creating a logical representation of the structure of the database The most important task in database development

3. © 2002 by Prentice Hall 3 Entity-Relationship Model (E-R Model) An Entity-Relationship Model (E-R Model) consists of: –Entities –Attributes –Identifiers –Relationships

4. © 2002 by Prentice Hall 4 An Entity An entity is an object that can be identified in the users’ work environment & that users want to track. Entities of a given type are grouped into entity classes.

5. © 2002 by Prentice Hall 5 An Entity Example

6. © 2002 by Prentice Hall 6 Attributes An attribute describes a characteristic of an entity For example –An entity: Employee –Has attributes: EmployeeName Extension DateOfHire

7. © 2002 by Prentice Hall 7 Identifier An identifier uniquely identifies a row in a table. For an Employee, the SocialSecurityNumber may serve as the Indentifier.

8. © 2002 by Prentice Hall 8 Relationships A relationship describes how one or more entities are related with each other.

9. © 2002 by Prentice Hall 9 Relationship Cardinality Entity-Instance Participation in relationships is shown by –maximum cardinality –minimum cardinality

10. © 2002 by Prentice Hall 10 Maximum Cardinality The maximum cardinality indicates/depicts the maximum number of instances involved in a relationship. Alternatives include –1:1 (one-to-one) –1:N (one-to-many) –N:M (many-to-many)

11. © 2002 by Prentice Hall 11 Relationship Examples Showing Maximum Cardinality Alternatives

12. © 2002 by Prentice Hall 12 Minimum Cardinality The minimum cardinality indicates/depicts whether participation in the relationship is mandatory or optional. Alternatives include –0 (optional) –1 (mandatory)

13. © 2002 by Prentice Hall 13 A Relationship Example Showing Minimum and Maximum Cardinality

14. © 2002 by Prentice Hall 14 A Recursive Relationship A recursive relationship is when an entity has a relationship with itself.

15. © 2002 by Prentice Hall 15 Entity-Relationship Diagram (E-R Diagram) An entity-relationship diagram (E-R Diagram) is a graphical representation of the E-R model using a set of ‘somewhat’ standardized conventions

16. © 2002 by Prentice Hall 16 An Entity-Relationship Diagram (E-R Diagram) Example

17. © 2002 by Prentice Hall 17 Weak Entity A weak entity is an entity whose instance survival depends (logically) on an associated instance in another entity

18. © 2002 by Prentice Hall 18 Subtype Entities Some entities may have many common attributes and a few unique attributes. The common attributes may be grouped together in a supertype entity and the unique attributes may be grouped together in a subtype entity.

19. © 2002 by Prentice Hall 19 CLIENT with Subtype Entities

20. © 2002 by Prentice Hall 20 E-R Diagram Computer Assisted Software Engineering (CASE) Tools Several Computer Assisted Software Engineering (CASE) Tools exist to help create E-R Diagrams and the resulting physical database elements. Products include: –IEW –IEF –DEFT –ER-WIN –Visio

21. © 2002 by Prentice Hall 21 Unified Modeling Language (UML) The Unified Modeling Language (UML) is a set of structures and techniques for modeling and designing object-oriented programs (OOP) and applications. A primary difference between UML & E-R Diagrams is that the UML representation includes information about object constraints and methods

22. © 2002 by Prentice Hall 22 E-R Diagram Example: Jefferson Dance Club

23. © 2002 by Prentice Hall 23 E-R Diagram Example: San Juan Charters

24. © 2002 by Prentice Hall 24 David M. Kroenke Database Processing Eighth Edition Chapter 3 The Entity- Relationship Model