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Chapter 3 Data Modeling

Chapter 3 Data Modeling. Fundamentals of Database Management Systems by Mark L. Gillenson, Ph.D. University of Memphis Presentation by: Amita Goyal Chin, Ph.D. Virginia Commonwealth University John Wiley & Sons, Inc. Chapter Objectives.

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Chapter 3 Data Modeling

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  1. Chapter 3Data Modeling Fundamentals of Database Management Systems by Mark L. Gillenson, Ph.D. University of Memphis Presentation by: Amita Goyal Chin, Ph.D. Virginia Commonwealth University John Wiley & Sons, Inc.

  2. Chapter Objectives • Explain the concept and practical use of data modeling. • Recognize which relationships in the business environment are unary, binary, and ternary relationships. • Describe one-to-one, one-to-many, and many-to-many unary, binary, and ternary relationships.

  3. Chapter Objectives • Recognize and describe intersection data. • Model data in business environments by drawing entity-relationship diagrams that involve unary, binary, and ternary relationships.

  4. Essence of Data Modeling • Exploring the different ways that entities can relate to each other as they always do in the real world • Devising a way of recording, of diagramming, the entities and the ways in which they interrelate in the business environment

  5. Entity-Relationship (E-R) Model • A diagramming technique • Diagrams entities (with attributes) and the relationship between the entities. • There are many variations of E-R diagrams in use.

  6. E-R Model Entity (and its attributes) • Rectangular shape • Salesperson = a type of entity • Name of entity is in caps above the separator line.

  7. E-R Model Entity (and its attributes) • Entity type’s attributes are shown below the separator line. • An asterisk denotes attribute(s) that constitute the entity type’s unique identifier.

  8. Relationships • Associations between entities • Different kinds: • Binary relationships • Unary relationships • Ternary relationships

  9. Binary Relationships • Simplest kind of relationship • Relationship between two entity types • Diamond-shaped box represents relationship • A salesperson “sells” products or products are sold by salespersons

  10. Cardinality • Represents the maximum number of entities that can be involved in a particular relationship. • One-to-One Binary Relationship • One-to-Many Binary Relationship • Many-to-Many Binary Relationship

  11. One-to-One Binary Relationship • 1-1 • A single occurrence of one entity type can be associated with a single occurrence of the other entity type and vice versa.

  12. One-to-Many Binary Relationship • 1-M • Use “crow’s foot” to represent the multiple association. • “many” = the maximum number of occurrences that can be involved, means a number that can be 1, 2, 3, ... n.

  13. Many-to-Many Binary Relationship • M-M • “many” can be either an exact number or have a known maximum.

  14. Cardinality

  15. Modality • The minimum number of entity occurrences that can be involved in a relationship. • “inner” symbol on E-R diagram (“outer” symbol is cardinality)

  16. Cardinality & Modality

  17. Intersection Data • Describes the relationship between two entities. • Used with many-to-many relationships. • Represented on E-R diagram in a special five-sided intersection data box, which is attached to the relationship diamond between the two entity boxes.

  18. Many-to-Many Binary Relationship with Intersection Data • For example, we know not only that salesperson 137 sold some of product 24013 but also how many units of that product that salesperson sold.

  19. Associative Entity • Entities can have attributes; many-to-many relationships can have attributes. • Many-to-many relationship may be treated similarly to entities in an E-R diagram.

  20. Associative Entity • Should you diagram as associative entity or many-to-many relationship? • personal taste • follow company standards • The unique identifier of the associative entity is usually the combination of the unique identifiers of the two entities in the many-to-many relationship.

  21. Unary Relationships • Associate occurrences of an entity type with other occurrences of the same entity type. • Cardinality: • One-to-One Unary Relationship • One-to-Many Unary Relationship • Many-to-Many Unary Relationship

  22. Unary Relationships

  23. Ternary Relationship • Involves three different entity types.

  24. Ternary Relationship: The General Hardware Company E-R Diagram • Customer Employee, a dependent entity, is distinguished by a diagonal hash mark in each corner of its attribute area.

  25. Good Reading Bookstores

  26. World Music Association

  27. Lucky Rent-A-Car

  28. “Copyright 2004 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information contained herein.”

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