24
HNDComputing – DeMontfort University Ó DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 D a t a b a s e D e s i g n C o n c e p t Database Design Concepts IMAT1408 Lecture 4 Worked Example of ER Modelling

HNDComputing – DeMontfort University DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

Embed Size (px)

DESCRIPTION

HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design Concepts 3 To create an ER Model You would use the results of your fact finding to identify the entities (as we discussed last week) In this case we will use a scenario Identify the entities from the scenario on the next slide……….

Citation preview

Page 1: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

Database Design ConceptsIMAT1408

Lecture 4

Worked Example of ER Modelling

Page 2: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

2

Objectives

We will use another simple scenario and identify:– The entities– The relationships between the entities – The multiplicity of each relationship

We will see that ER modelling is an iterative process.

Page 3: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

3

To create an ER Model• You would use the results of your fact finding to identify the entities (as we discussed last week)• In this case we will use a scenario• Identify the entities from the scenario on the next slide……….

Page 4: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

4

The Scenario• A small cinema club runs a number of cinemas throughout the region. The cinemas show films. A film is shown several times over a week or more in a series of showings. Members book for a particular showing.• Identify the entities.

Page 5: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

5

• A small cinema club runs a number of cinemas throughout the region. The cinemas show films. A film is shown several times over a week or more in a series of showings. Members book for a particular showing.

Page 6: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

6

Draw a Box for each Entity

Page 7: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

7

Refer back to the scenario and identify relationships

• A small cinema club runs a number of cinemas throughout the region. The cinemas show films

• A film is shown several times over a week or more in a series of showings

• Members book for a particular showing.

Page 8: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

8

A possible relationship

• cinemas show films.

• You could draw that like this:

showsCinema Film

Page 9: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

9

Another possible relationship

• film is shown … in … showings.

Film

screens

Showing

Showing

screened

Film

OR……

is

at

Page 10: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

10

Always draw a joined-up diagram(draw each entity once)

Cinema Film

screened

Showing

shows

is

at

Page 11: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

11

Now add this relationship

• Members book for a ……showing

Cinema Film

screened

Showing

shows

Memberbooks

for

is

at

Page 12: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

12

This is a first attempt – expect changes later!

• We have used the verbs in the scenario to get us started

• We may find later that these are not the best relationships to put in our diagram

• ER modelling is iterative: sometimes we draw many versions before we are satisfied

• Carry on for now………..

Page 13: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

13

Identify the multiplicity of each relationship: cinema-shows-film

• How many cinemas can a film be shown at? • How many films can a cinema show?• Does a cinema have to show a film in order to be on our database as a cinema?• Does a film have to be shown at a cinema in order to be on our database?

Page 14: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

14

• How many cinemas can a film be shown at? Many • How many films can a cinema show? Many• So the relationship is many to many• Does a cinema have to show a film in order to be on our

database as a cinema? Let’s say “No”, it’s non-obligatory (We are making an assumption here)

• Does a film have to be shown at a cinema in order to be on our database? Let’s say “Yes”, it’s obligatory

Page 15: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

15

MMCinema Film

screened

Showing

shows

Memberbooks

for

is

at

Page 16: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

16

• A showing screens how many films?• A film can have how many showings?• Must a film have a showing to be on the database?• Must a showing have a film to be on the database?

Identify the multiplicity of each relationship: is-screened-at

Page 17: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

17

• A showing screens how many films? 1• A film can have how many showings?

Many• Must a film have a showing to be on the database? Yes - obligatory• Must a showing have a film to be on the database? Yes – obligatory.

Page 18: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

18

MMCinema Film

screened

Showing

shows

Memberbooks

for

is

at

M

1

Page 19: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

19

Identify the multiplicity of each relationship: books-for

• How many showings can a member book for? • How many members can book for a showing? • Must every showing have a member booked for

it? • Must every member have booked for a

showing?

Page 20: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

20

• How many showings can a member book for? Many• How many members can book for a showing? Many• Must every showing have a member booked for it? No, non-obligatory• Must every member have booked for a showing? No, non-obligatory.

Page 21: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

21

MMCinema Film

screened

Showing

shows

Memberbooks

for

is

at

M

1

M M

Page 22: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

22

We have not finished!• We will see in week 6 that this is only a first attempt at a system design for the cinema club• There are problems with this diagram and we can do better• Don’t forget that ER modelling is an iterative process…………

Page 23: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

23

Summary• We have:

• Identified entities and relationships between the entities• Drawn an ER diagram to show the entities and relationships• Recorded the multiplicity of each relationship• Used the Chen notation which is standard on this module.

Page 24: HNDComputing – DeMontfort University  DeMontfort University 2011 Entity Relationship Modelling (continued) wk4 Database Design ConceptsDatabase Design

HNDComputing – DeMontfort University Ó DeMontfort University 2011

Entity Relationship Modelling (continued) wk4D

atabase Design Concepts

24

Reference• Data Analysis for Database Design

By D R Howe