7. sequence and collaboration diagrams

Sequence and Collaboration Diagrams

Chapter 7

Object-Oriented Software Systems Engineering – Chapter 7 Slide 1

Objectives

In this chapter we will:
 Review the different dynamic modelling
techniques
 Discuss different types of messages
 Discuss different types of events
 Introduce sequence and collaboration diagrams


Dynamic Modelling

 Dynamics of a system
 how objects communicate and the effects of such
communication
 how objects collaborate through communication and how
objects change state
 Dynamics of a system is described by four diagrams
State Sequence
Collaboration Activity

 Interaction
 communication between objects in order to generate some
function
 described in sequence, collaboration and activity diagrams


Dynamic Modelling diagrams

 State diagram -describes
 which states an object can have
 behaviour in those states
 what events cause the state to change

 Sequence diagram - describes how objects
interact and communicate with each other
 primary focus is time
 shows how a sequence of messages are sent and
received between a set of objects in order to perform
some function


Dynamic Modelling diagrams

 Collaboration diagram - describes how objects
interact
 focus is on space - relationships between objects are
shown

 Activity diagram - describes activities and their
order - another way of showing interactions
 focus on work - when objects interact they also perform
work in terms of activities


Dynamic Modelling - Messages

 Message
 a communication between objects that conveys
information
 has a sender and recipient
 is represented as an arrow denoting flow of control


Dynamic Modelling - Messages

 Types of messages
 simple
flat flow of control - control is passed
without describing any details
 synchronous
nested flow of control - operation call
handling of the message is completed
before the caller resumes execution
 asynchronous
there is no explicit return to the caller
the sender continues to execute after
sending the message without waiting
for it to be handled


Dynamic Modelling

 Use cases are elaborated in two stages
 Expand the use-cases into sequence diagrams
 Use the sequence diagrams to produce finite state
machines


Events

 Kinds of events
 receipt of a call on an operation by another object
( message)
 the signal itself is an object-shown as an event-signature
on state transitions
 receipt of an explicit signal from another object
(message)
 the signal itself is an object- also shown as an event-
signature on state transitions
 a condition becoming true
 shown as a guard condition
 passage of a designed period of time
 shown as a time expression


Events

 Basic semantics about event labeled transitions
 events are triggers that activate state transitions
 if an event can activate more then one transition only one
will be triggered
 if en event occurs and guard is false then the event is
ignored (events are not stored)


Dynamic Modelling-Sequence Diagram

:Object A :Object B

:Actor A
Focus of control

Simple message

Synchronous
message return

Objects lifeline

Asynchronous
messge
destructor()

Object is destroyed X


Sequence Diagram

:A :B :C

[ x>0 ] doM()

[ x<=0 doN()]
 Conditional branch

:A :B

 Loop
*dialDigit(d)


Sequence Diagram
 To support conditional and looping constructs, the UML
uses frames. Frames are regions or fragments of the
diagrams; they have an operator or label (such as loop) and
a guard (conditional clause).
 The following table summarizes some common frame
operators:

Frame
Operator Meaning
alt Alternative fragment for mutual exclusion
conditional logic expressed in the guards.
loop Loop fragment while guard is true.
opt Optional fragment that executes if guard is true.
par Parallel fragments that execute in parallel.
region Critical region within which only one thread can run.


Sequence Diagram Example

:floor panel :ElevatorControl :floorSensor :Elevator
<<boundary>> <<control>> <<boundary>>
Person on floor
Call(floorNumber)

state idle

moveUp(floorNumber)

arriveAt(floorNumber)
state moving up
stop()

state idle



:floor panel :ElevatorControl :floorSensor :Elevator
<<boundary>> <<control>> <<boundary>>
Person on floor
Call(floorNumber)

state idle

moveDown(floorNumber)

arriveAt(floorNumber)
state moving down
stop()

state idle



:ElevatorControl :floorSensor :Elevator
<<control>> <<boundary>>

state idle
[timer=time_out]/moveDown(firstfloor)

arriveAt(firstfloor)
state moving down to first floor

stop()

state on first floor


Dynamic Modelling - Collaboration Diagram

 Show:
 network of collaborating objects
 interactions
- how messages are sent between objects
 Used to illustrate execution of
 a use case
 an operation
 Focus on time


Collaboration Diagram

: User
: Queue

6: printing
1: print( file )

2: print( file) 3: print( file )
: Computer : Print : Printer
Server
5: printing 4: printing


Collaboration Diagram

: User
: Queue

1: print( file ) 3: store( file ) 4: stored
6: wait

2: print( file)
: Computer : Print : Printer
Server
5: wait


Collaboration Diagram for ElevatorControl

 On further investigation ElevatorControl may
need to be expanded into more classes
 revisit sequence diagrams!

:ElevatorControl

1: Call floor(number)
1.1: *[all queues]:len=length(){return shortest} 2: nextjob=get()
:Queue :Dispatcher
:Organiser
1.3:Invoke(job){join queue}

1.2:Create()
parameter

Active object
own thread
:Order of control


More about Interaction Diagrams

 Different developers have different preferences
 time-ordering or spatial
 Interaction diagrams are good at showing
collaboration between objects
 They are not good at precise definition of the
behaviour
 They are at their best when the behaviour is simple
 To capture complex behaviour in a single diagram
use an activity diagram
 To look at the behaviour of a single object across
 many use cases use a state diagram
 many use cases or many threads use an activity diagram


Summary

In this chapter we have:
 Reviewed the different dynamic modelling
techniques
 Discussed different types of messages
 Discussed different types of events
 Introduced sequence and collaboration diagrams


7. sequence and collaboration diagrams

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