1. Case Studies: Data Modeling
SEEM3430: Information Systems Analysis and Design

2. Case 1: Description each lecturer tutors a group of students
A university consists of a number of
departments. Each department offers several courses. A number of modules make up each course. Students enrol in a particular course
and take modules towards the completion
that course. Each module is taught by a lecturer from the appropriate department,
each lecturer tutors a group of students of
and
Entity Relationship Modelling

3. Identify Entities departments. Each department offers several
A university consists of a number of
departments. Each department offers several
courses. A number of modules make up each course. Students enrol in a particular course and take modules towards the completion of that course. Each module is
taught by a lecturer from the appropriate department, and each lecturer tutors a group of students
Entity Relationship Modelling

4. Identify Relationships•
A university consists of a number of
departments. Each department offers several courses. A number of modules make up each course. Students enrol in a particular course and take modules towards the completion of that course. Each module is taught by a
lecturer from the appropriate department, and each lecturer tutors a group of students
Entity Relationship Modelling

5. Example - E/R Diagram Entities: Department, Course, Module, Lecturer,
Student
Course
Module
Lecturer
Student
Entity
Relationship Modelling

6. Example - E/R Diagram Each department offers several courses
Module
Lecturer
Student
Entity Relationship Modelling

7. Example - E/R Diagram A number of modules make up each courses
Department
courses
Offers
Course
Includes
Module
Lecturer
Student
Entity Relationship Modelling

8. Example - E/R Diagram Students enrol in a particular course Department
Offers
Department
Course
Includes
Module
Lecturer
Enrols In
Student
Entity Relationship Modelling

9. Example - E/R Diagram Students … take modules Department Course Module
Offers
Department
Course
Includes
Module
Lecturer
Takes
Enrols In
Student
Entity Relationship Modelling

10. Example - E/R Diagram Each module is taught by a lecturer Department
Offers
Course
Includes
Module
Teaches
Lecturer
Takes
Enrols In
Student
Entity Relationship Modelling

11. Example - E/R Diagram a lecturer from the appropriate department
Offers
Department
Employs
Course
Includes
Module
Teaches
Lecturer
Takes
Enrols In
Student
Entity Relationship Modelling

12. Example - E/R Diagram each lecturer tutors a group of students
Offers
Department
Employs
Course
Includes
Module
Teaches
Lecturer
Takes
Enrols In
Student
Tutors
Entity Relationship Modelling

13. Example - E/R Diagram Department Course Module Lecturer Student Offers
Employs
Course
Includes
Module
Teaches
Lecturer
Takes
Enrols In
Student
Tutors
Entity Relationship Modelling

14. Entities and Attributes facts about • Sometimes it is hard
to tell if something should be an entity •
General guidelines •
Entities can have
attributes but attributes have no smaller parts
Entities can have relationships between them, but an attribute belongs to a single entity or •
an attribute
They both
objects or the world
represent
facts about • •
They are both often
represented by nouns in descriptions
Entity Relationship Modelling

15. Case 2: Supplier/Product
We want to represent information about
products in a database. Each product has a description, a price and a
supplier. Suppliers have addresses,
phone numbers, and names. Each address is made up of a street address, a city, and a postcode.
Entity Relationship Modelling

16. Indentify Entities/Attributes phone number • Entities or attributes: •
Products, suppliers,
and addresses all have smaller parts so we can make them entities
The others have no smaller parts and belong to a single entity •
product
description
price
supplier
address
phone number
name
street address
city
postcode •
Entity Relationship Modelling

17. Example - E/R Diagram Product Supplier Address Price Description
Street address
Name
Supplier
Address
City
Phone number
Postcode
Entity Relationship Modelling

18. Identify Relationships supplier address single supplier but address •
Each product has
supplier a •
Each supplier has an
address •
Each product has a
single supplier but •
A supplier has a single
address
It does not seem sensible for two
there is nothing
stop a supplier supplying many products
A many to one relationship to •
different suppliers
have the same address
A one to one relationship to • •
Entity Relationship Modelling

19. Example - E/R Diagram Product Supplier Address Price Description Has A
Street address
Name
Supplier
Has A
Address
City
Phone number
Postcode
Entity Relationship Modelling

20. One to One Relationships between A and B • Some relationships •
Example - the
supplier-address relationship
between entities,
and B, might be redundant if A •
Is one to one
Every supplier has address
We don’t need addresses that are •
It is a 1:1 relationship
between A and B an •
Every A is related
B and every B is related to an A to a •
not
related to a supplier
Entity Relationship Modelling

21. Redundant Relationships a entity • We can merge the two entitiesx
two entities
take part in redundant relationship
that a b A B y c z
together
• They become a single
entity
• The new entity has all the attributes of the old one a x b AB y c z
Entity Relationship Modelling

22. Example - E/R Diagram Product Supplier Price Description Has A Name
City
Phone number
Postcode
Street address
Entity Relationship Modelling

23. Tips: E/R Diagrams diagram and then the relationships •
From a description
the requirements identify the of •
Draw the E/R
diagram and then •
Look at one to one
relationships as they might be redundant
Look at many to
many relationships as they might need to be split into two one to many links •
Entities
Attributes
Relationships
Cardinality ratios
the relationships • of
Entity Relationship Modelling