1. Activity Diagrams
Chapter 6
Object-Oriented Software Systems Engineering – Chapter 6 Slide 1

2. Objectives
In this chapter we will:
 Introduce Activity Diagrams
 Discuss where activity diagrams are used
Object-Oriented Software Systems Engineering – Chapter 6 Slide 2

3. Activity Diagrams
 Use activity diagrams in the context of
 system as whole
 a subsystem
 an operation
 Model dynamic aspect of a system in two ways
 a workflow -- to visualise , specify, construct, and
document business processes
 an operation -- to model the details of a computation
involved with parameters of the operations and its local
objects
Object-Oriented Software Systems Engineering – Chapter 6 Slide 3

4. Activity Diagrams
 Activity
 a sort of state which is left by the previous activity
 activity can involve many steps, including waiting for
events
 Transition
 an arrow line without label
 actions are included in activities rather than on the
transition
 Synchronisation bar
 describing the co-ordination of activities
 waiting for all the subtasks to finish before proceeding
(join),
 starting several subtasks in parallel (fork)
Object-Oriented Software Systems Engineering – Chapter 6 Slide 4

5. Activity Diagrams
 Decision activity
 an alternative to guard conditions on separate transitions
leaving the same state
 Swimlanes and partitions
 several groups of related activities
 these activities are related according to which objects or
actors perform them
 Start and stop
Object-Oriented Software Systems Engineering – Chapter 6 Slide 5

6. Activity Diagrams
Decision activity
Activity 1 Activity 2
[condition 1]
start [condition 2]
Activity 3
Activity 4 Activity 5
Synchronisation bar
stop
Object-Oriented Software Systems Engineering – Chapter 6 Slide 6

7. Activity Diagrams - modelling workflow
 Establish a focus for the workflow to show all
interesting activities in one diagram
 Select the business objects that have high-level
responsibility for the parts of the overall workflow,
and each important business object is associated
with a swimlane
 Identify the pre-conditions and post-conditions of
the workflow
 Specify the activities and actions that take place
over time
Object-Oriented Software Systems Engineering – Chapter 6 Slide 7

8. Activity Diagrams - modelling workflow
 Provide a separate activity diagram to expand
complicated actions or set of actions
 Consider branching activities with forking and
joining
 There are more advanced features
Object-Oriented Software Systems Engineering – Chapter 6 Slide 8

9. Activity Diagrams - modelling an operation
 Collect the abstractions that are involved in the
operation (parameters, return type, attributes)
 Identify pre & post conditions & any invariants
 Beginning at the operations initial state, specify
the activity & actions that take place over time &
render them in an activity diagram as either
activity states or action states
 Use branching as necessary to specify conditional
paths and iteration
 Use forking and joining as necessary to specify
parallel flows of control
Object-Oriented Software Systems Engineering – Chapter 6 Slide 9

10. Activity Diagrams - Example
[joined bank]
log on
second level
authorisation
make manage
payment instruction
Object-Oriented Software Systems Engineering – Chapter 6 Slide 10

11. Library Users Librarian Activity diagrams
[borrow] Find book Example
on shelf
[return]
Wait in
queue
[returning]
[borrowing]
Record Put book
return back on shelf
Spot the mistakes!
Record
borrowing
Prepare for
next user
Object-Oriented Software Systems Engineering – Chapter 6 Slide 11

12. Customer Sales Warehouse
Request product
Process order Pull materials
Ship order
Receive order Bill customer
Pay bill
Activity diagrams
Close order
- Example
Object-Oriented Software Systems Engineering – Chapter 6 Slide 12

13. Activity diagrams
- Example 4
[grade >= 40]
print “Failed”
[false]
[true]
print “Passed”
Object-Oriented Software Systems Engineering – Chapter 6 Slide 13

14. Activity Diagrams - Example
[grade >= 40]
print “Failed”
[false]
[true]
print “Passed”
Object-Oriented Software Systems Engineering – Chapter 6 Slide 14

15. More About Activity Diagrams
 Suitable for:
 Analysing a use case
 Understand what actions need to take place
 Describe the behavioural dependencies between objects
 Allocate operations to objects within interactive diagrams
 Understanding workflow across many cases
 Representing use cases interacting with each other
 Dealing with multithreaded applications
 Not suitable for:
 Trying to see how objects collaborate – use collaboration
diagrams instead
 Trying to see how an object behaves over its lifetime –
use state diagrams instead
Object-Oriented Software Systems Engineering – Chapter 6 Slide 15

16. Summary
In this chapter we have:
 Introduced Activity Diagrams
 Discussed where activity diagrams are used
Object-Oriented Software Systems Engineering – Chapter 6 Slide 16