1 Content A.Software development cycleSoftware development cycle B.What are objects?What are...

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Content

A. Software development cycle

B. What are objects?

C. Deriving objects from a given problem

D. Generalization / Specialization

E. Case Studies

F. Appendix : a Diagram with different Names ?

Unit 2 : Problem Solving Through Object

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A) SDLLC - Software Development LifeLife Cycle

well-defined steps to handle & manage development

it avoids :

1. problems in coordinating many developers & many programs on a large project

2. miscommunication between developers & users SDC is cyclical, not linear also called 'waterfall model'

pp-3

3

RequirementPhase

AnalysisPhase

DesignPhase

ImplementationPhase

TestingPhase

Maintenance

It’s also called a WaterFall Model

Simplified SDC model

4

According to nature of common activities in s/w development, it is divided into 6 phases: 1. Requirements phase 2. Analysis phase 3. Design phase 4. Implementation phase 5. Testing phase 6. 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.

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RequirementPhase

AnalysisPhase

DesignPhase

ImplementationPhase

TestingPhase

Maintenance

RequirementPhase

AnalysisPhase

DesignPhase

ImplementationPhase

TestingPhase

RequirementPhase

AnalysisPhase

DesignPhase

ImplementationPhase

TestingPhase

……

…

An Iterative approach

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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

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Pipelining

RequirementPhase

AnalysisPhase

DesignPhase

ImplementationPhase

TestingPhase

RequirementPhase

AnalysisPhase

DesignPhase

ImplementationPhase

TestingPhase

Time

Project -A

Project -B

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

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A Completed SDC Diagram

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

pp-9

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Requirement

Phase

AnalysisPhase

DesignPhase

ImplementationPhase

TestingPhase

Maintenance

Normal process flow

meetneeds

meetneeds

meetneeds

meetneeds

meetneeds

Y

Y

Y

Y

Y

N

N

N

N

N

Something wrong ?

Go back to appropriate phase(s)

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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)

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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

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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.

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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

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Deliverable produce requirement specifications 1. list of roles of the users of the software

eg, in banking, users are customer, teller, supervisor & manager

2. 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.

3. 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

4. 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

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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

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3) Design phase

Previously, developers analysis a system in business viewpointObjectives 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

behaviorDeliverable List of classes, each with a list of attributes and behaviors

(with well-defined steps ) is produced

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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

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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

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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

6) Maintenance phase pp-9

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B) What are objects ?

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“

pp-10

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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.

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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

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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.

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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

Class Name

Attributes

Behaviors

divided into three regions - class name attributes

that each object of this class has behaviors

that each object of this class has

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WashingMachine

brandName : StringmodelNumber : Stringcapacity : doubletimeRequired : doubleconsumptionRate : doubleheight : doublewidth : doubledepth : double

start ( )top ( )setTimer ( hour : int )getTimeElapsed ( ) : int

wM : WashingMachine

brandName = “ABC”modelNumber = “WM-201”capacity = 5timeRequired = 45consumptionRate = 50height = 880width = 530depth = 530

start ( )top ( )setTimer ( hour : int )getTimeElapsed ( ) : int

Class definition Object instances

': int' indicates the returns

feedback of type integer

Class Name

Attributes

Behaviors

Data Types

: WashingMachine

brandName = “ABC”modelNumber = “XYZ”capacity = 5timeRequired = 45consumptionRate = 50height = 880width = 530depth = 530

start ( )top ( )setTimer ( hour : int )getTimeElapsed( ) : int

object name is wM

An anonymous object(object name is optional)

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The Given Requirements

1. 'Start Washing' button of washing machine is pressed

2. The incoming water valve is opened for 5 minutes.

3. The drum motor starts at normal speed for 15 minutes.

4. The outgoing water valve is opened.

5. The drum motor starts at high speed for 5 minutes.

6. The outgoing water valve is closed.

7. The incoming water valve is opened for 5 minutes.

8. The drum motor starts at normal speed for 15 minutes.

9. The outgoing water valve is opened.

10. The drum motor starts at high speed for 5 minutes.

11. The outgoing water valve is closed.

pp-15

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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.

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:WashingMachine

:OutgoingValve

Modeling the washing Machine Objects

:DrumMotor:IncomingValve

1 : wash ( )

3, 8 : startNormalSpeed (15)

5, 10 : startNormalSpeed ( 5)

4, 9 : open ( )

6, 11 : close ( )

2, 7 : open (5)

pp-16

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Interaction among objects

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

pp-17~8

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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.

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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.

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Textual Analysis

Given a problem statement

find objects by highlighting (or underlining) the nouns and noun phrases

the steps are: 1. Determine the involved objects (and the classes)

2. Determine the object attributes

3. Determine the object behaviors

4. 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.


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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 ?

Y

N

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

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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

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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

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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.

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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.

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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


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 BankAccount

not an Entity but still useful

both SRC & DES are accounts, so Group them

as BankAccount Class

all CamelStyle

copy all nouns from the requirement statement

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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


:Bank

source:BankAccount

destination:BankAccount1 : transfer (source, destination, amount )

2 : withdraw (amount)

3 : deposit (amount)

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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:

eg. transfer $ between accounts (Design Phase)

BankAccount

balance : double

withdraw ( amount : double)deposit ( amount : double)

Bank

transfer ( source : BankAccount , destination : BankAccount , amount : double )

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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

Directorname : StringstaffNumber : StringcalculateSalary( ) salary : double

Clerkname : StringstaffNumber : StringcalculateSalary( ) salary : double

Managername : StringstaffNumber : StringcalculateSalary( ) salary : double

Director

commission : double

calculateSalary( ) salary : double

Clerk

otPayRate : double


Manager

allowance : double


Staff

name : StringstaffNumber : StringcalculateSalary( ) salary : double

generalizing common attributes / behaviors

eg. name

specialized bysome specific attributes / behaviors

eg. commissionsuper class

subclass

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By Inheritance, subclass inherits all attributes/behaviors

superclass Clerk, Manager, Director will inherit everything from

superclass Staff : the attributes “name” & “staffNumber” & the behavior “calculateSalary”

Director

commission : double


Clerk

otPayRate : double


Manager

allowance : double


Staff

name : StringstaffNumber : String


Inheritance & Method Overriding

By Method Override, subclass define & use

its behaviors overriding the inherited ones from super class

Overriding Staff’s method to

handle OT pays

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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

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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 :

Animal

weight : doubleage : doublelifeLength : double

eat( )sleep( )move( )reproduce( )

Lion elephant Bird

fly( )

Lizard Snake

Hawk Owl

Top level

Middle level

general class super class, base class,parent class

specific class subclass, derived class,child class

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E) Case Studies

With courteous of Vicmon FAN (group-8), please refer to his Web Version as follows :

[ http://learn.ouhk.edu.hk/~t430859/mt201/note/unit2/noteUnit2-2.htm ]

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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

F) Appendix - a Diagram with different Names ?

( Out syllabus )

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