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CSE323
การวิเคราะห์ และออกแบบระบบ
(Systems Analysis and Design)
Lecture 07:
Object Interaction and
Specifying Operations
1
Object Interaction
2
Object Interaction –
Communication Diagrams & Interaction
Overview Diagrams
Timing Diagrams
Based on Chapter 9 of Bennett, McRobb and
Farmer:
Object Oriented Systems Analysis and Design
Using UML, (3rd Edition), McGraw Hill, 2005.
3
In This Lecture You Will Learn:
Object Interaction and Collaboration
CRC Cards
how to model object interaction using an
interaction communication diagram.
how to model interactions using interaction
overview diagrams;
how to model interaction using an interaction
sequence diagram;
how to use timing diagrams.
4
Object Interaction & Collaboration
Message Passing
Objects communicate by sending messages
When an object sends a message to another object,
an operation is invoked in the receiving object
The aim of modelling object interaction is to
determine the most appropriate scheme of message
passing between objects to support a particular user
requirement
5
Object Interaction & Collaboration
Appropriate distribution of object responsibility
improves software modularity
Each class tends not to be unduly complex, and as a
result is easier to develop, to test and to maintain.
Each class is relatively small and self-contained, and
as a result has a much greater potential for reuse.
The system is more resilient to changes in its
requirements
A modular system is easier
to be maintained and upgraded
to achieve high reliability
to be implemented in small, manageable increments
6
Aug-12 7
CRC Cards
Class–Responsibility–Collaboration (CRC) cards help to
model interaction between objects
Brainstorm the classes
Allocate each class to a team members
For each use case, role play the interaction to distribute
responsibilities among classes:
• each object identifies the object that he/she thinks is most
appropriate to take on a needed responsibility for collaboration
• each object should be as lazy as possible, refusing to take on
any responsibility unless persuaded by its fellow objects
8
CRC Cards
Class Name:
Responsibilities Collaborations
Responsibilities of a class Collaborations with other
are listed in this section. classes are listed here,
together with a brief
description of the purpose
of the collaboration.
9
CRC Cards
Aug-12 10
Dynamic Analysis with UML
Communication Diagrams
Sequence Diagrams
Interaction Overview Diagrams
Timing Diagrams
In UML 1.x,
communication diagrams are called collaboration diagrams.
In UML 1.x,
interaction overview diagrams and timing diagrams do not exist.
11
Communication Diagrams
Hold the same information as sequence
diagrams.
Show links between objects that participate
in the collaboration.
No time dimension, sequence is captured
with sequence numbers.
Sequence numbers are written in a nested
style (for example, 3.1 and 3.1.1) to indicate
the nesting of control within the interaction that
is being modelled.
12
Communication Diagrams
Notations
Message order is captured with sequence numbers, which are
written in a nested style (for example, 3.1 and 3.1.1) to indicate
the nesting of control within the interaction that is being
modelled.
:Campaign anAdvert:Advert
getCost
currentAdvertCost = anAdvert.getCost()
13
Message Labels
Type of message Syntax example
Simple message. 4: addNewAdvert
Nested call with return value. 3.1.2: name = getName
The return value is placed in the
variable name.
Conditional message. 5 [balance > 0]: debit(amount)
This message is only sent if the
condition [balance > 0] is true.
Iteration 4.1 *[For all adverts]: getCost
14
Aug-12 15
Sequence Diagrams
Purpose
A sequence diagram shows an interaction between
objects arranged in a time sequence.
Sequence diagrams can be drawn at different levels
of detail and to meet different purposes at several
stages in the development life cycle.
Sequence diagrams are typically used to represent
the detailed object interaction that occurs for one use
case or for one operation.
16
Sequence Diagrams
Notations
Objects (or subsystems or other connectable
objects) involved in interaction appear horizontally
across the page and are represented by lifelines.
The execution or activation of an operation is
shown by a rectangle on the relevant lifeline.
17
Sequence Diagrams
Notations
Messages are usually shown by a solid horizontal arrow.
• A synchronous message or procedural call is shown with a full
arrowhead, causes the invoking operation to suspend execution
until the focus of control has been returned to it.
• It is optional to show reply messages (with dashed arrows)
because it can be assumed that control is returned to the
originating object at the end of the activation in a destination object
(except for asynchronous messages).
• A reflexive message that an object sends to itself is shown by a
message arrow that starts and finishes at the same object lifeline.
18
Sequence Diagrams
Combined Fragments
Sequence
• Vertical dimension shows time.
Iteration (looping) is shown by a combined fragment rectangle
with the interaction operator ‘loop’.
• The loop combined fragment only executes if the guard condition in
the interaction constraint evaluates as true.
Selection (branching) is shown by a combined fragment
rectangle with the interaction operator ‘alt’ (a short form of
alternatives).
• The alt combined fragment has two (or more) compartments known
as operands. Each operand corresponds to one of the alternatives
in the combined fragment and each operand should have an
interaction constraint to indicate under what conditions it executes.
19
Sequence Diagrams
Notations
Object creation is shown with the construction
message (dashed arrow) going to the object symbol.
Object destruction is indicated by a large X on the
lifeline on the destruction point.
20
Sequence Diagrams
Aug-12 21
Interaction Overview Diagrams
Variants of activity diagrams
Focuses on the flow of control in an interaction
Nodes in the diagram may be interactions or
interaction occurrences
Interaction needs to be broken down into its
key elements.
22
Interaction Overview Diagrams
An alternative version of the sequence
diagram Add a new advert to a campaign
if within budget is shown on the next slide
and is used to develop an interaction
overview diagram
23
sd Add a new advert to a campaign if within budget
:CampaignManager
:Client :Campaign :Advert
getName
listCampaigns ref
List client campaigns
ref
Get campaign budget
addCostedAdvert
alt [totalCost <= budget]
ref
Create advert
[else]
ref
Create request
24
Interaction Fragment Used
sd Get campaign budget
:CampaignManager :Campaign :Advert
checkCampaignBudget
loop [For all campaign’s adverts]
getCost
getOverheads
25
Interaction Fragment Used
sd Create advert
:Campaign :Advert
Advert
newAd:Advert
26
Interaction Fragment Used
sd Create request
:Campaign :Advert
Request newRequest:Request
27
sd Add a new advert to a campaign if within budget
sd List Campaigns for Client
:CampaignManager
:Client :Campaign
getName
listCampaigns
loop [For all client’s campaigns]
getCampaignDetails
Initial node
ref
Get campaign budget
Interaction occurrence In-line sequence
sd Add costed advert diagram
:Campaign
:CampaignManager
addCostedAdvert
Decision
[totalCost <= budget] [totalCost > budget]
ref ref
Create advert Create request
28
Final node
Timing Diagrams
A new feature in UML 2.0
Show how time constraints affect interactions
between lifelines
The sequence diagram Car enters car park is
the basis for the subsequent timing diagram
29
Timing Diagrams
sd Car enters car park
before:WeightSensor :TicketMachine :Barrier after:WeightSensor
activate
Lowered
Active
ticketRequested
raiseBarrier
deactivate
Raised
Blocked lowerBarrier
Lowered
barrierLowered
Inactive
30
Timing Diagrams
Sloped line
represents duration
of state change
sd Car enters car park lifelines :Barrier, :TicketMachine
Diagram has two
Timing
instances, one for :Barrier
Raised
Constraint
{t..t+3s}
each lifeline
Lowered
barrierLowered
:TicketMachine
Blocked raiseBarrier
Active
Message from one
lifeline to another Inactive
t
31
Model Consistency
Timing diagrams must be consistent with the
relevant sequence diagrams and state
machines.
32
Summary
In this lecture you have learned about:
how to model object interaction using an
interaction communication diagram.
how to model interactions using interaction
overview diagrams;
how to model interaction using an interaction
sequence diagram;
how to use timing diagrams.
33
Specifying Operations
34
OBJECTIVES
To understand :
why operations need to be specified
The difference between algorithmic and
non – algorithmic methods
How to interpret different ways of specifying
operations
How to specify operations using one method.
35
In this chapter you will learn :
How to use :
- Decision Tables
- Pre and post-condition pairs
- Structured English
- Activity Diagrams
- Object Constraint Language
36
Why we specify operations
From analysis perspective :
- Ensure user needs are understood
From design perspective :
- Guide programmer to an appropriate
implementation (i.e. method)
From test perspective :
- verify that the method does what was
originally intended
37
Types of Operation and Their effects
Operations with side-effects may:
- Create or destroy object instances
- Set attribute values
- Form or break links with other objects
- Carry out calculations
- Send messages or events to other objects
- Any combination of these
Operations without side-effects are pure queries
- Request data but do not change anything
38
Services Among Objects
When objects collaborate one object
typically provides a service to another
Examples :
- A client object might ask a campaign
- Structured English
- Activity Diagrams
- Object Constraint Language
39
Contracts: an approach to defining services
A service can be defined as a contract
between the participating objects
Contracts focus on inputs and outputs
Intervening process is seen as a black box
Irrelevant details are hidden
This emphasizes service delivery, and
ignores implementation
40
Contract-Style Operation Specification :
Intent or purpose of the operation
Operation signature, including return type
Description of the logic
Other operations called
Events transmitted to other objects
Any attributes set
Response to exceptions
(e.g. an invalid parameter)
Non-functional requirements
41
Types of Logic Specification
Logic description is probably the most
important element.
Two main categories:
Algorithmic types are white box – they
focus on how the operation might work
Non-algorithmic types are black box –
they focus on what the operation
should achieve.
42
Non-Algorithmic Techniques
Appropriate where correct result matters
more than method to arrive at it
Decision tree: complex decisions, multiple
criteria and steps (not described further here)
Decision table: similar applications to
decision tree
Pre- and Post-condition pairs: suitable where precise
logic is unimportant or uncertain
43
Example Decision Table
Conditions and actions Rule 1 Rule 2 Rule 3
Conditions
Is budget likely to be overspent?
N Y Y
Is overspend likely to exceed 2%? - N Y
Actions
No action X
Send letter X X
Set up meeting X
44
Algorithmic Techniques
Suitable where users understand the
procedure for arriving at a result
Can be constructed top-down, to handle arbitrarily
complex functionality
Examples:
- Structured English
- Activity Diagrams
45
Structured English :
Commonly used, easy to learn
Three types of control structure,
derived from structured programming:
- Sequences of instructions
- Selection of alternative instructions
(or groups of instructions)
- Iteration (repetition) of instructions
(or groups of instructions)
46
Sequence in Structured English
Each instruction executed in turn, one after
another
get client contact name
sale cost = item cost * ( 1 - discount rate )
calculate total bonus
description = new description
47
Selection in Structured English
One or other alternative course is
followed, depending on result of a test :
if client contact is ‘A’
set discount rate to 5%
else
set discount rate to 2%
end if
48
Iteration in Structured English
Instruction or block of instructions is
repeated
- can be a set number of repeats
- or until some test is satisfied, for example
do while there are more staff in the list
calculate staff bonus
store bonus amount
end do
49
Activity diagram
Are part of UML notation set
Can be used for operation logic specification, among
many other uses
Are easy to learn and understand
Have the immediacy of graphical notation
Bear some resemblance to old-fashioned flowchart
technique
50
Simple activity diagram
Create new Link to
StaffGrade CreativeStaff
Link to previous
StaffGrade
Set previous
StaffGrade
gradeFinishDate
Figure 10.2 an activity diagram show the main steps for the operation
51
Activity diagram with selection
[not approved
by Director]
Check approval Print approval
for grade change request
[approved by Director]
Create new Link to
StaffGrade CreativeStaff
Link to previous
StaffGrade
Set previous
StaffGrade
Figure 10.3 A more complex activity diagram gradeFinishDate
52
Activity Diagram with Selection
and Iteration
Calculate bonus
Create [bonus < £25] [bonus > £250]
warning Add to ‘star’ list
letter
[bonus >= £25 AND
bonus <= £250]
Add to list
[more StaffMembers]
[no more StaffMembers]
Format list
Figure 10.4 activity diagram
53
Activity diagram for creativestaff.
calculatebonus()
Find oldest
Campaign
Worked on
Get campaign
Bonus level
Set bonus to
Grade
minimum
Get next
campaign
Average
Campaign
Bonus level
54
Activity diagram for the use case check
campaign budget.
Get client Show campaign
[correct Campaign] [incorrect Campaign]
Get Advert cost
Calculate
Overheads
[no more Adverts] [more Adverts]
Figure 10.6 activity diagram for the use case check campaign budget
55
Object Constraint Language
Most OCL statements consist of:
- Context, Property and Operation Context
- Defines domain within which expression
is valid
- Instance of a type, e.g. object in
class diagram
- Link (association instance) may be a context
A property of that instance
- Often an attribute, association-end or query
operation
56
Object Constraint Language
OCL operation is applied to the property
Operations include
- Arithmetical operators *, +, - and /
- Set operators such as size, isEmpty
and select
- Type operators such as oclIsTypeOf
57
OCL expression Interpretation
Person In the context of a specific person, the
value of the property ‘gender’ of that
self.gender
person—i.e. a person’s gender.
Person The property ‘savings’ of the person
self.savings >= 500 under consideration must be greater
than or equal to 500.
Person If the set ‘husband’ associated with a
self.husband-> notEmpty implies person is not empty, then the value of
self.husband.gender = male the property ‘gender’ of the husband
must be male. Boldface denotes OCL
keyword, but has no semantic import.
Company The size of the set of the property ‘CEO’
of a company must be less than or
self.CEO->size <= 1
equal to 1. That is, a company cannot
have more than 1 Chief Executive
Officer.
Company The set of employees of a company
whose age is less than 60.
self.employee->select (age < 60)
58
OCL Used for Pre and post -
conditions
context CreativeStaff::changeGrade
(grade:Grade, gradeChangeDate:Date)
pre:
grade oclIsTypeOf(Grade)
gradeChangeDate >= today
post:
self.staffGrade[grade]->exists
self.staffGrade[previous]->notEmpty
self.staffGrade.gradeStartDate = gradeChangeDate
self.staffGrade.previous.gradeFinishDate =
gradeChangeDate
59
Summary
In this lecture you have learned about:
The role of operation specifications
What is meant by “Contracts”
Algorithmic and non-algorithmic techniques,
and how they differ
How to use:
- Decision Tables, Pre- and Post-condition Pairs,
Structured English, Activity Diagrams and
Object Constraint Language
60
References :
Bennett, McRobb and Farmer (2002)
Yourdon (1989) covers Structured English
and Pre- and Post-conditions well
Senn (1989) is good on Decision Tables
Larman (1998) takes a contract-based
approach to O-O analysis and design,
with examples taken to Java code
(For full bibliographic details, see Bennett, McRobb and
Farmer)
61
Next Lecture
System Architecture
Aug-12
CSE323 62
Systems
