1. Unit 2 : Problem Solving Through Object
3/27/2017
Content
Software development cycle
What are objects?
Deriving objects from a given problem
Generalization / Specialization
Case Studies
Appendix : a Diagram with different Names ?
Dear all,
I’ll be glad if you can start making up your own REVISION NOTES by consolidating as much POINTS that available, such as my notes, other tutors notes, other fellow students’ notes.
As a graduated student of OUHK, I wish both teaching staff & students have OPEN minds – info sharing -- but not your TMAs :P
Kenny YUEN
========
PS: Special THANKS for Vicmon FAN [ ], who has summarized most important points for me make up this version

2. A) SDLC - Software Development Life Cycle
pp-3
well-defined steps to handle & manage development
it avoids :
problems in coordinating many developers & many programs on a large project
miscommunication between developers & users
SDC is cyclical, not linear
also called 'waterfall model'

3. Simplified SDC model Requirement Phase Analysis Phase Design Phase
It’s also called a
WaterFall Model
Analysis
Phase
Design
Phase
Implementation
Phase
Testing
Phase
Maintenance

4. Simple software : a single pass may suffice
According to nature of common activities in s/w development, it is divided into 6 phases:
Requirements phase
Analysis phase
Design phase
Implementation phase
Testing phase
Maintenance phase
Simple software : a single pass may suffice
Sophisticated software might be too complicated to build with a single pass through these 6 phases.
A single pass might only complete a portion of the features (or a software module) of the system.

5. An Iterative approach Maintenance Requirement Phase Analysis Phase
Design
Phase
Implementation
Phase
Testing
Phase
Requirement
Phase
Analysis
Phase
Design
Phase
Implementation
Phase
Testing
Phase … … …
Requirement
Phase
Analysis
Phase
Design
Phase
Implementation
Phase
Testing
Phase
Maintenance

6. An Iterative approach
the entire software development is divided into iterations.
Each iteration aimed at a portion of the system and each iteration takes all except Maintenance phase
iterates, cycle-by-cycle until system tested OK, moving to Maintenance Phase
no. of cycles varies as
system complexity &
developers’ decision
eg.
it finished in 5 cycles
with a spiral view

7. Pipelining
Example : while some developers are working on the testing phase of an iteration, another group of developers has already started working on the requirement phase for the next iteration. 
complete more projects in shorter time
Project -A
Requirement
Phase
Analysis
Phase
Design
Phase
Implementation
Phase
Testing
Phase
Project -B
Requirement
Phase
Analysis
Phase
Design
Phase
Implementation
Phase
Testing
Phase
Time

8. A Completed SDC Diagram
pp-9
When expected output of a phase does not meet the users’ requirements, either
back to its prior phase ( 1 step back ), or
back to earlier phases ( some steps back )
eg. In Implementation, when some info is missing :
Programmer ask a Designer, who may go back to the Design Phase & re-design the system, or
the Designer ask an Analyst, who may go back to Analysis Phase & clarify user requirements
After clarifying the info, resume normal process
So, a complete SDC model must allow going back to 1 or more phase(s) when necessary

9. Go back to appropriate phase(s)
Requirement
Phase
meet
needs
Analysis
Phase N Y
Normal process flow
meet
needs
Design
Phase N Y
meet
needs
Implementation
Phase N Y
meet
needs
Testing
Phase
Go back to appropriate phase(s)
Something wrong ? N Y
meet
needs
Maintenance N Y

10. OO approach to Software Development
s/w developers try to model real-world scenarios & system operations by objects.
relationship between classes & objects
a class definition is defined for
objects with same type, and
entities with same attributes & behaviors
When an application is executed, the relevant class definitions are used to create objects so that the objects have the appropriate attributes and behaviors.
so a class is a blueprint for a group of objects of the same category, eg.
made cookies (object) from CookieCutter (Class)

11. 1) Requirements phase (SDC Activities)
Objectives
collect requirements (needs) from user/client who request for software (s/w) development.
“needs” refer to functionalities of the software,
Requirements may include software limitations
sample requirements of a payroll system
what types of staff are to be supported,
what types of payment method are required, etc.
limitations are constraints of the software, such as hardware, time limits & budget.
eg. users may require a response time < 3 sec,
finish the s/w on Linux platform, in 3 months without exceeding a budget of HK$ 20,000

12. From time to time, developers seek users’ clarification Deliverables
Activity
interview the
client, who requested the s/w, and
end user, who’ll use the s/w
Common problem is miscommunication between client/user & developer because :
users use business terminology (jargon), &
developer have little business knowledge.
From time to time, developers seek users’ clarification
Deliverables
developer prepare a problem statement, which summarizes all user requirements, including software limitations
a problem statement help user & developer clarify the needs & limitations early in s/w development.

13. 2) Analysis phase Objectives
to understand operational details for each user requirement
focus on what a system must do
Activity
to identify functionalities & features of the software based on the problem statement from requirements phase

14. Deliverable produce requirement specifications
list of roles of the users of the software
eg, in banking, users are customer, teller, supervisor & manager
list of functionalities or operations for each role
eg, in a banking, account operations are deposit, withdraw & transfer.
allow Teller to perform all these operations, but
only Supervisors can modify transactions made by tellers.
list of operational scenarios under different conditions
allow withdraw operation, if account has enough money
else, reject the withdraw operation & the s/w alerts user
list of business entities with their attributes & behaviors
a transfer operation involves 2 accounts + a transaction record.
account has an attribute, 'balance', and 2 operations, deposit & withdraw

15. If not enough information was collected, repeat the requirement phase
Remarks
these 2 phases (requirement & analysis) are programming language independent because
their Objectives is to collect user requirements &
to understand the operational details.
If not enough information was collected, repeat the requirement phase
until thoroughly clear about
what the users expect and
the details of all functionalities

16. 3) Design phase
Previously, developers analysis a system in business viewpoint
Objectives
transform requirements into technical design
model real-world cases & system operations by objects
Design class definitions (re-use in implementation phase)
Activity
From requirement specification, find attributes of objects
Objects of the same type, and entities with same behaviors & attributes, are defined as a single class.
consolidate Operational scenarios to well-defined steps of behavior
Deliverable
List of classes, each with a list of attributes and behaviors (with well-defined steps ) is produced

17. 4) Implementation phase
Objectives
aims at converting the class designs derived in the design phase to actual class definitions in the chosen programming language.
Activity
use Java (in our course) to implement
the classes, their attributes and behaviors
Deliverable
method bodies
program codes which are ready for testing

18. 5) Testing phase Objectives
to make sure the programs do what we expected
uncover software errors before releasing it to users
Activity
verify programs by
feed in test data and then
check if outputs match expected results.
If un-matching, codes are examined & checked for errors
After errors are found / corrected, programs are re-tested
This process is repeated until all errors are corrected
Deliverable
a readily deployable software system

19. 6) Maintenance phase
pp-9
Objectives
to fix the errors found after deployment
in large & sophisticated system, not all errors can be found / corrected at testing phase
in adapting to a rapidly changing world, software need to be enhanced / enriched for users to continue using
Activity
involves code modification, which may take much effort for improperly designed/implemented software
maintenance cost will > the sum of prior 5 phases.
That’s why we need a systematic way to build software
Deliverable
an updated software with fixed errors & enhanced feature

20. B) What are objects ? Real-World Objects (RWO)
pp-10
Real-World Objects (RWO)
Our world is made up of objects
a chair, a television set, a computer
everything are objects.
desktop/personal computer (PC) & notebook computer are in the same category “Computer“
they are characterized by attributes such as
hard disk & RAM size, CPU type/speed
In OO, we call such a category a class. So, PCs are instances (or objects) of the class “Computer“

21. Software objects (SO)
OO software use SO to model RWO, both physical things and abstract concepts or ideas.
SO has attributes to mimic characteristics of RWO
SO has behaviors that correspond to the actions of RWO
RWO may have many characteristics & actions
SO model only a subset of them for a specific problem. Thus, the same RWO may be modeled differently in different software.
SO only exist while a s/w is running. The object states must be stored properly so that they can be recreated the next time when the software is run.

22. Object concepts attributes vs. states
attributes = properties of an object
states = values of properties of an object
which reflect current situation of the object
objects always have attributes, and
their values (or states) may change over time, especially if they are manipulated in any ways
the value of an attribute determines the current state of an object

23. message vs. behaviour
in a software system, an object will never perform its behavior unless we send a message to it
message type & object behavior is 1→1 mapping
If an object has a behavior such as ‘doSomething ’, it is expected that it can
accept a message type ‘doSomething ’ and
perform the ‘doSomething ’ behaviour.

24. Class Diagram for a Washing Machine
Attributes & behaviors of a washing machine object are identified in analysis phase.
In design phase, a class definition is used to describe / model a washing machine object
divided into three regions -
class name
attributes
that each object of this class has
behaviors
Class Name
Attributes
Behaviors

25. Class definition Object instances wM : WashingMachine : WashingMachine
object name is wM
An anonymous object
(object name is optional)
Class Name
Data Types
Attributes
WashingMachine
wM : WashingMachine
: WashingMachine
brandName : String
modelNumber : String
capacity : double
timeRequired : double
consumptionRate : double
height : double
width : double
depth : double
brandName = “ABC”
modelNumber = “WM-201”
capacity = 5
timeRequired = 45
consumptionRate = 50
height = 880
width = 530
depth = 530
brandName = “ABC”
modelNumber = “XYZ”
capacity = 5
timeRequired = 45
consumptionRate = 50
height = 880
width = 530
depth = 530
start ( )
top ( )
setTimer ( hour : int )
getTimeElapsed ( ) : int
start ( )
top ( )
setTimer ( hour : int )
getTimeElapsed ( ) : int
start ( )
top ( )
setTimer ( hour : int )
getTimeElapsed( ) : int
Class definition
Object instances
Behaviors
': int' indicates the returns feedback of type integer

26. The Given Requirements
pp-15
'Start Washing' button of washing machine is pressed
The incoming water valve is opened for 5 minutes. 
The drum motor starts at normal speed for 15 minutes. 
The outgoing water valve is opened. 
The drum motor starts at high speed for 5 minutes. 
The outgoing water valve is closed. 
The outgoing water valve is closed.

27. Accomplishing tasks by objects
In OO programming, tasks always involve objects.
To complete a task, we expect
some results will be returned from the objects or
the states of some objects will be changed.
Suppose the objects WashingMachine, DrumMotor, IncomingValve and OutgoingValve have been found to be appropriate.
The washing operation can be accomplished by messages sent among the objects.

28. Modeling the washing Machine Objects
pp-16
:WashingMachine
3, 8 : startNormalSpeed (15)
5, 10 : startNormalSpeed ( 5)
2, 7 : open (5)
4, 9 : open ( )
6, 11 : close ( )
:IncomingValve
:OutgoingValve
:DrumMotor
Modeling the washing Machine Objects

29. Interaction among objects
pp-17~8
behaviors of an object are not performed unless it receives a message
the only interaction among objects is the messages sent among them
While sending a message from Sender to Receiver, the Sender assume that the Receiver can :
understand this message &
perform a behavior according to this message
Sender concerns What the Receiver will do
Sender doesn’t concern How a Receiver works
Receiver can determine its own way to perform a behavior according to this message

30. Benefit of such interaction among objects
capability of handling complexity
every object (the agent) is only required to perform its own operations based on the attributes and the supplementary data in the messages (parameters) when it receives particular messages.
Each object performs its own part.
All objects cooperate, and they constitute a complex operation.
It is much easier for analysts to :
clarify a single operation of an object than
analysis all scenarios when many objects are involved in a complex operation.

31. C) Deriving objects from a given problem
core activity in analysis phase
identify object/class and their attributes & behaviors from the problem statement
more than 1 result may be derived, it depends on our understanding on the problem and our trade-offs
eg. pp-29, methods can be defined in 2 ways.
there is no fixed rule to select the best way
Regardless of the derived result, make sure that
the derived objects can fully model all scenarios.

32. Textual Analysis Given a problem statement
find objects by highlighting (or underlining) the nouns and noun phrases
the steps are:
Determine the involved objects (and the classes)
Determine the object attributes
Determine the object behaviors
Verify if the list of objects & behaviors is complete or not
The bank system transfers an amount of money from a source account to a destination account. It first withdraws the amount from the source account and then deposits the same amount in the destination account.
The bank system transfers an amount of money from a source account to a destination account. It first withdraws the amount from the source account and then deposits the same amount in the destination account.

33. Step 1 & 2: Identify Object/Class & Attributes
nouns (& noun phases) can be :
objects / Class or
object attributes or.
duplicated (already identified) object, or
irrelevant to our model.
determination criteria :
Noun
an Entity ? Y N
Candidate Object / Class
Object Attributes
relevant ?
Discard it
if we interest in modeling the thing itself, then model it as separate class
for things that we are not interested but are helpful properties of some classes, then treat them as attributes

34. After grouping & filtering the nouns & noun phrases, we have a list of
The decision to consider whether it is necessary to model an object by class definition is based on our understanding of the problem, so there is no concrete answer. 
group the nouns of the same type of entity and
give it a class name
After grouping & filtering the nouns & noun phrases, we have a list of
class names
Don’t use plural nouns. ( No “s” )
all CamelStyle (capitalize 1st letter of each word)
and their attributes
start with lowercase letter &
use CamelStyle to concatenate the rest

35. Finally, determine whether
an object comprises other identified objects or
an object has other objects as its components
CPU = CU + ALU + Reg ( ref : Von Neumann arch.)
if an object has attribute for each component object,
then give a name to each one. 
if an object always sends messages to some objects,
then the corresponding class definition has an attribute for each of them.
WashingMachine has attributes (components) of
IncomingValve,
OutgoingValve and
DrumMotor

36. Step 3: Identify Object Behaviors
generate a list of potential object behaviors by identifying verbs & verb phases in the problem statement
if 2 different verbs are referring to the same behavior,
then choose any one of them. 
check which object(& class) has these behaviors
eg. state changes or action taken
some verbs only specify that
an object has attributes (rather than behavior)
the output in this step is a list of object behaviors that we can add to the related classes.

37. Step 4 : check completeness of objects & behaviors
Analysis the scenarios when messages are sending among objects. Verify/check whether :
object behaviors suffice to model the scenarios, &
supplementary info is needed to perform the behavior
Is the list of objects & behaviors ( it ) complete ?
if we can model the original scenario based on a sequence of object behaviors,
then it is complete
this also marks the end of the analysis phase
if it cannot cooperate to finish a task,
then it may be incomplete
we have to re-analysis the problem & review it. 

38. eg. transfer $ between accounts (Analysis Phase)
highlighting / underlining nouns & noun phrases
Build table
check entries in 1st column, for candidate Classes,
if yes give a class name in 2nd column 'Class name'
else write comments on 3rd column
The bank system transfers an amount of money from a source account to a destination account. It first withdraws the amount from the source account and then deposits the same amount in the destination account.
not an Entity but still useful
copy all nouns from the requirement statement
all CamelStyle
Object / Class
Class Name
Remarks
amount
Supplementary info of behavior
amount of money
Same as amount (duplicated)
bank system
Bank
destination account
BankAccount
source account
both SRC & DES are accounts, so Group them as BankAccount Class

39. destination:BankAccount
highlight Verb & Verb Phases
To draw our diagram
use the 2nd column of our table, draw all Classes
draw arrows according to our highlighted behaviors
label all arrows with the name of the behaviors
label all arrows with their operational sequence
filling supplementary data / parameters
The bank system transfers an amount of money from a source account to a destination account. It first withdraws the amount from the source account and then deposits the same amount in the destination account.
source:BankAccount
2 : withdraw (amount)
:Bank
3 : deposit (amount)
1 : transfer (source, destination, amount )
destination:BankAccount

40. eg. transfer $ between accounts (Design Phase)
a bank account should maintain its own balance
So, an attribute balance is added to it.
to facilitate Java implementation we have to consider some language-specific issues, like data type.
Thus, double, which can keep real numbers, is chosen for the attribute balance & all the related behaviors.
the resulted class definitions:
Bank
transfer ( source : BankAccount ,
destination : BankAccount ,
amount : double )
BankAccount
balance : double
withdraw ( amount : double)
deposit ( amount : double)

41. D) Generalization & Specialization (gen-spec)
Given 3 similar classes differ by name only
By generalization (a new class Staff is created)
gen-spec are 2 sides of the same coin
Clerk
Manager
Director
name : String
staffNumber : String
name : String
staffNumber : String
name : String
staffNumber : String
calculateSalary( )
salary : double
calculateSalary( )
salary : double
calculateSalary( )
salary : double
specialized by
some specific
attributes / behaviors
eg. commission
generalizing common attributes / behaviors
eg. name
Staff
name : String
staffNumber : String
calculateSalary( )
salary : double
super class
subclass
Clerk
Manager
Director
otPayRate : double
allowance : double
commission : double
calculateSalary( )
salary : double
calculateSalary( )
salary : double
calculateSalary( )
salary : double

42. Inheritance & Method Overriding
By Inheritance,
subclass inherits all attributes/behaviors superclass
Clerk, Manager, Director will inherit everything from superclass Staff :
the attributes “name” & “staffNumber” &
the behavior “calculateSalary”
By Method Override,
subclass define & use its behaviors overriding the inherited ones from super class
Staff
name : String
staffNumber : String
calculateSalary( )
salary : double
Overriding Staff’s method to handle OT pays
Clerk
Manager
Director
otPayRate : double
allowance : double
commission : double
calculateSalary( )
salary : double
calculateSalary( )
salary : double
calculateSalary( )
salary : double

43. Advantages
Whatever changes to the super class’s attributes & behaviors, those changes will apply to subclasses
Thus, minimizes the maintenance efforts of attributes and behaviors
enables programs to be written to manipulate general Staff objects
since objects of subclasses {Clerk, Manager, Director} can be treated as objects of super class {Staff}, so subclasses can accept the same messages and perform the behaviors that a super class object accepts (even though subclasses may have method overriding)
Then, it is convenient to send the same message calculateSalary to every Staff object, and they will calculate their own salaries properly. This is called polymorphism

44. Class Hierarchy At top-level,
Since Animal defines all attributes & behaviors, so Animal is a general class while the others are specific classes,
middle level, Bird plays dual roles
specific class of Animal
general class of Hawk & Owl
arrow draws from specific to general
Remarks :
Top level
Animal
weight : double
age : double
lifeLength : double
eat( )
sleep( )
move( )
reproduce( )
Middle level
general class
super class,
base class,
parent class
specific class
subclass,
derived class,
child class
Lion
elephant
Bird
fly( )
Lizard
Snake
Hawk
Owl

45. E) Case Studies
With courteous of Vicmon FAN (group-8), please refer to his Web Version as follows :
[ ]

46. F) Appendix - a Diagram with different Names ?
Object Interaction Diagram (p-22)
Operational Diagram (p-47)
Message Sending Diagram (p-49)
anyway it looks like “Collaboration Diagram” in UML
ref. pp-89, The UML Ref Manual, Addison Wesley, 1999
UML = Unified Modeling Language
( Out syllabus )