Database Design & Implementation
Workshop 4 – Drawing ER Diagrams
• Draw Degree, Type & Participation diagrams that depict each
of the following relatively simple ‘real-world’ situations:
a) A member of staff must work in a department, and there are
many members of staff in each department.
b) Several buses can park in the garage, and each bus may cover
any number of routes.
c) Each producer is in charge of several plays and there are
several actors appearing in each play. At any one time an actor
may be involved in more than one play.
d) An operator can work on many machines and each machine has
many operators. Each machine belongs to one department, but
a department can have many machines.
ER Diagram Elements
Entity
Entity = a singular noun, enclosed in a box.
Relationship = a solid line, with rounded ends.
type =>
<= type
Type = a verb, or verb phrase.
NB. MUST indicate the Type in BOTH directions.
1
Degree = only two possibilities.
M
Compulsion = a vertical line, within an Entity.
a) A member of staff must work in a department, and there
are many members of staff in each department.
Staff
Works in =>
M <= Employs 1
Department
b) Several buses can park in the garage, and each bus may
cover any number of routes.
1
Bus
M
parks in =>
<= holds
1
Garage
M
M
Bus/route
follows route =>
1
Route
<= is followed by
c) Each producer is in charge of several plays and there are several actors
appearing in each play. At any one time an actor may be involved in
more than one play.
Producer
produces =>
1
<= produced by
M
Play
1
features =>
M
Pla/Ac
1
<= appear in
M
Actor
d) An operator can work on many machines and each machine
has many operators. Each machine belongs to one
department, but a department can have many machines.
Operator
M
works on =>
M
1
Op/Mach
Machine
<= Has many
M
<= Has many
<= Belongs to
1
1
Department
Begin the process of producing the ER
Diagram that forms 40% of Assignment 1
• by:
– Identifying ALL of the Entities; by reading the Case Study
carefully.
– Drawing Occurrence diagrams; in order to explore the
Relationship between each Pair of Entities you have identified.
– Testing the Relationship between each Pair of Entities; against
one, or more, of the 10 questions at the back of the Case Study.
• If you CAN NOT ‘answer’ all 10 of the questions, then
you HAVE NOT:
– either; identified ALL of the Entities.
– and/or; explored ALL of the necessary Relationships.