1 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Session 6 Designing a Database ITE 252 Database Management

2 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Homework HW#1: Create an E-R diagram modeled after the Good Reading Bookstores E-R diagram (Figure 3-19 in your text and slide 14 here) for a publisher of music (limit to MP3s). Draw the diagram by hand and write up a description similar to the one in section (pp.95-95) in your text. Due next class

3 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Designing Relational Tables Typical process for converting E-R diagrams to relational tables: – Each entity converts to table – For many-to-many relationships, each associative entity converts to table – Attributes become table columns – Ensure foreign keys appear in proper places in tables To convert single entity, create table of same name with column for each attribute

4 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Salesperson Entity and Table

5 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Converting Binary Relationships Greater importance in selecting identifier and primary key – Identifier and primary key define foreign key that establishes relationships between tables Often more than one way to represent entity relationships as relational tables

6 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Example: Converting 1-1 Binary Relationship

7 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Example: Converting 1-1 Binary Relationship

8 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Example: Converting 1-1 Binary Relationship

9 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Example: Converting 1-1 Binary Relationship Converting one-to-one Salesperson/Office relationship – Options: Convert relationship to single/combined table Convert relationship to two tables

10 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Example: Converting 1-1 Binary Relationship Considerations: – Business environment considers Salesperson and Office as separate entities – Modality of zero at Salesperson entity in E-R diagram (office may have no one assigned) – Salesperson entity in E-R diagram has relationships with other entities

11 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Example: Converting 1-1 Binary Relationship Solution 1: – Combine two entities into one table

12 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Example: Converting 1-1 Binary Relationship Solution 2: – Two separate tables – Office Number as foreign key in Salesperson table

13 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Example: Converting 1-1 Binary Relationship Solution 3: – Two separate tables – Salesperson Number as foreign key in Office table

14 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting 1-M Binary Relationship

15 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting 1-M Binary Relationship Each occurrence of Salesperson is related to zero or more occurrences of Customer Unique identifier of entity on “one” side is placed as foreign key in entity of “many” side

16 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting 1-M Binary Relationship

17 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting M-M Binary Relationship

18 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting M-M Binary Relationship Most relational DBMS systems DO NOT directly support many-to-many relationships Solution: Include associative entity to establish relationship May use composite key as primary key in associative entity A key that is defined by multiple columns is called a composite key

19 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting M-M Binary Relationship

20 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting M-M Binary Relationship not required

21 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting 1-1 Unary Relationship

22 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting 1-1 Unary Relationship With: – Only one entity type involved, and – One-to-one relationship Conversion requires only one table

23 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting 1-M Unary Relationship each salesperson manages zero or more salespersons each salesperson is managed by a manager

24 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting 1-M Unary Relationship each salesperson is managed by a manager

25 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting M-M Unary Relationship Many-to-many unary relationship: – For example: one product can be constructed out of set or subset of other products – General rule in conversion: Number of tables equal to number of entity types plus one more table for many-to-many relationship – M-M unary relationship - 2 tables – M-M binary relationship - 3 tables – M-M ternary relationship - 4 four tables

26 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting M-M Unary Relationship

27 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management Example: Converting M-M Unary Relationship

28 Nassau Community CollegeProf. Vincent Costa Acknowledgements: Introduction to Database Management, All Rights ReservedIntroduction to Database Management international, open membership, not- for-profit technology standards consortium. Homework Read Chapter 4.1- pp