programming paradigms seminar 3

Seminar 3: Making Good Progress

Programming Paradigms

[The Paradigms - Group 2]

We will always use system analysis and design at the start of every software project.

Analysis

Design

ImplementationTesting

Maintenance

Well-done analysis and design Reduce risk

No approaches were taught to derived

Their properties

Their responsibilities

Critical classes

Knowing an good approach can build a robust system design.

Let us learn an approach to do system analysis and design

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What is Object-Oriented Analysis & Design?

An approach that models a system as a group of interacting objects.

Teacher Student

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New approach to analysis & design

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CRC Approach

What is CRC?

Class, Responsibility & Collaboration

1. Discovering the real world objects is a system

2. Mapping the collaboration among classes and their responsibilities

Why CRC?

Uses brainstorming and role-playing to maximize advantages of group work

Basics of CRC approach

OO Characteristics

Knowing CRC Card

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OO CharacteristicsAbstraction“Eliminate the Irrelevant,

Amplify the Essential”

Encapsulation“Hiding the Unnecessary”

Inheritance“Modeling the Similarity”

Polymorphism“Same Function Different Behavior”

ClassName , SubclassesResponsibilities Collaboration

The things they do Their relationship to other classes

Back of the card is used list attributes and write class description

StudentdoHomework Teacher

The things they do Their relationship to other classes

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QuickCRC

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CRC books

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6. Identifying Hierarchy

5. Assigning Collaborators

4. Assigning Responsibilities

3. Selecting Core Classes

2. Clarifying the Scope

1. Discovering Candidate Classes

CRC Card

1. Read Requirements Documents

2. Underline nouns and noun phrases.

3. Add them to candidate class list.

4. Brainstorm to find other potential classes.

CRC Card




The ATM System will interface with the customer through a display screen , numeric and special input keys, a bankcard reader, a deposit slot, and a receipt printer.

Customer may make deposits, withdrawals and balance inquires using the ATM machine, but the update of accounts will be handled by an interface to the Accounts system.

Customers will be assigned a PIN and clearance level by the security system which will be verified prior to transactions.

We would allow customers to update routine information such as change of address or phone number using the ATM.

1. Read Requirements Documents1.Discovering The Candidate Class List

The ATM System will interface with the customer through a display screen , numeric and special input keys, a bankcard reader, a deposit slot, and a receipt printer.

Customer may make deposits, withdrawals and balance inquires using the ATM machine, but the update of accounts will be handled by an interface to the Accounts system.

Customers will be assigned a PIN and clearance level by the security system which will be verified prior to transactions.

We would allow customers to update routine information such as change of address or phone number using the ATM.

1. Discovering The Candidate Class List


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3. Add them to candidate class list. 1. Discovering The Candidate Class List

• ATM System • Customer• Display screen • Numeric • Special input keys• Bankcard reader• Deposit slot• Receipt printer• Deposits

• Withdrawals• Balance inquires• Accounts• PIN • Clearance level• Security system • Transactions• Change of address • Phone number

Candidate Class List

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Q: How does the customer access the ATM?

Bank Card

Bankcard reader

Numeric Key Pad

PIN



Candidate Class ListATM FinancialTransaction BankCardBankCustomer PIN AccountSavingsAccount CheckingAccount TransferWithdrawal Deposit BalanceInquiryReceipt ReceiptPrinter KeypadScreen CashDispenser ScreenMessageDisplay FundsAvailable DepositEnvelopeFailureBalance TimeOutKey TransactionLogKey AccountHolder PrinterScreenSaver Prompt NumericKey

1.Discovering The Candidate Class List

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CRC Card








Clarifying System Scope

What is and what is not part of the system.

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What is the scope of the ATM system?

QuestionsDoes it handle everything?•banking application•user interface•interactions between them

Does it.. • updates accounting

records?• records and mediates the

transaction activity?

Other Possible questions


ATM scope: Banking information capture

User interface & actual account update

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The sharper the system boundaries, the easier the evaluation of candidate class list.

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CRC Card








Critical Undecided Irrelevant

Sort Candidate Class List

Essential Classes for the application

BalanceInquiry

Withdrawal Deposit

Account



Class that we are NOT able to categorize without knowing the system boundaries and

definition



To be Reviewed further for categorization

Classes that are outside the system scope

Printer, ScreenSave, and Prompt. Related to the user interface subsystem But not to the core banking application



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Architectural Design Issues Eliminate Unnecessary Classes

1. Identify hot spots

2. Use appropriate design patterns

3. Take advantage of existing software frameworks

1. Remove ghost classes

2. Combine synonyms

3. Distinguish attributes from classes

What are Hot Spots?

A hot spot is a portion of the system that is likely to change from one system variant to another.

What are Hot Spots?

Hot spots encapsulate the variable aspects within components. Changes will only be made to hot spotsInterfaces and the relationships among

components will become less prone to changes.

Aid in designing components where changes is seldom necessary or constraint to a class

Identify Hot Spots

Identify hot spot by answering:• Which aspects of the domain differ fromapplication to application?

Let’s apply this question to our ATM domain ...

(Help to generate a List of hot spots)

Identify Hot SpotsAnalysis of ATMQ: Which aspects of the domain differ fromapplication to application?

Withdrawal handling. Why?

Future

Benefits of Hot Spots

Code Reuse

Architecture Reuse

Ease Changes

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2. Combine synonyms


Design Patterns

• A design pattern is a design structure that has been successfully used in a similar context

“No Point Reinventing the Wheel”“Reuse and Adapt existing”

Design Patterns

• Pioneers have laid out the foundations– There exist library of patterns

• Apply them to them to the CRC cards– Speed up analysis

Application of Design Patterns may result in new classes that are not found during brainstorming

“System Interaction Pattern"

AuthorizeSystemInteraction

Example

Encapsulate Communication between ATM and the bank existing security system

AuthorizeSystemInteraction

Example of Patterns that can be considered

• Clients• Servers• Transactions• Interacting Systems• Interacting Devices• Etc…

Some Good Pattern Books

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2. Combine synonyms


Framework

• A collection of classes that captures the architecture and basic operation of an application system.

• Systems are created by extending the given classes to add the specialized behaviors.

• Frameworks are "upside down libraries“.• System control resides in framework code

that calls "down" to user-supplied code.• A blue print for the implementation

Framework

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Example in ATM

• There are many papers on ATM that has been successfully built

• These framework can also be standards that existing ATM follows

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Part of a Framework

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In the event where there is no available framework

Use design patterns to aid the design and analysis part of the application

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2. Combine synonyms


Remove ghost classes

• Classes that do not fit within the application

• Classes that are related entities but are outside the system.

Example

Printer, and Keypad are relevant but outside the application.

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2. Combine synonyms


Combine synonyms

• Use a common name for same items

• This situation may arise when different groups within an organization use different names to refer to the same thing.

Similarity

BankCustomer and AccountHolder are probably synonyms.

Adopt one of them or create a new name.

Situation based

• Balance and FundsAvailable may or may not be different in concepts

Example:• A policy of disallowing withdrawals for some

period after deposit of a check.

Caution!

Be careful when the same word actually refers to different things!

New core classes may be needed.

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2. Combine synonyms


Distinguish attributes from classes

Some candidate classes may turn out to represent information only!

A candidate class may be an attribute if:– It does not have any operations– It does not change

Example

It does not have any operations

Balance and FundsAvailable - Few meaningful operations - Closely associated with Account.

Example

Cannot change stateConsider a PIN. If a PIN is viewed as being immutable, then it probably should be an attribute of Account.

BUTIf a PIN can change state (valid, invalid, and suspended), it should be a class.

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So what do we have so far?

Annotated Candidate Class List

Critical Classes• FinancialTransaction• Account• BalanceInquiry• Withdrawal• Deposit• AuthorizeSystemInterac

tion• BankCard

Undecided Classes• BankCustomer

(ghost - integrated with AuthorizeSystemInteraction)

• PIN (attribute)• SavingsAccount (attribute of Account)• CheckingAccount (attribute of

Account)• ATM (ghost -> system name)• FundsAvailable (attribute)• Balance (attribute)• AccountHolder (synonym)

Annotated Candidate Class List

Irrelevant Items• Transfer • Receipt• ReceiptPrinter• Keypad• Screen• CashDispenser• ScreenMessage• Display• Deposit

• EnvelopeFailure• TimeOut• KeyTransaction• LogPrinter• ScreenSaver• Prompt• Numeric Key• Key

Thank you!

End of Presentation

programming paradigms seminar 3

Documents

atm system

accounts system

system analysis

security system

robust system design

candidate class list1

candidate class list2

update of accounts