1. MODULE:VII OBJECT ANALYSIS: CLASSIFICATION
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2. Module VII Object Analysis:Classification
Recap: Objects
Objects are taken from the real world
They are abstract entities encapsulating data AND associated behaviour
Data is “protected” within individual chunks .Data Hiding.
Objects communicate (interfaces and messages)
“Design by contract”
objects make up the services offered by the system
eg: departments in an organisation
Objects are grouped into classes
Inherit from super class.
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3. The Use Case Driven Approach
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4. Classifications Theory
The process of checking to see if an object belongs to a category or a class, is regarded as a basic attribute of human nature.
Booch Explains:
Intelligence classification is part of all good science…Classification guides us in making decision about modularization.
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5. Classifications Theory…
We may choose to place certain classes and objects together in the same module or in different modules, depending upon the sameness we find among these declarations;
Coupling and cohesion are measures of this sameness.
Coupling also plays a role in allocating processes to procedures.
We place certain processes together in the same processor or different processors, depending upon packaging, performance, or reliability concern.
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6. Classifications Theory…
Classes are important mechanism for classifying objects. Eg: new car launched.
The chief role of a class is to define the attributes, methods and applicability of instances.
Classification is concerned more with identifying the class of an object than the individual objects within a system.—attributes.
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7. Module VII Object Analysis:Classification
Finding Classes
Finding classes is not easy.
The more practice you have, the better you get at identifying classes.
Finding classes is an incremental and iterative process.
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8. There is no such thing as the “right set of classes”
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9. Module VII Object Analysis:Classification
Finding Classes…
Unless you are starting with a lot of domain knowledge, you are probably missing more classes than you will eliminate.
Naming a class is also an important activity
The class should describe a single object, so it should be a singular noun or an adjective and a noun
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10. Finding Classes: User Involvement…
Make an adequate commitment of time. Iterative-still complete within time.
Have good warning of the time commitment that will be required of them
Be high-caliber workers who know their field or profession thoroughly
Be chosen from a variety of levels
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11. Module VII Object Analysis:Classification
Finding Classes…
Jacobson’s 3 types
Entity
Concrete—land,place
Conceptual—not tangible
Event and State
Interface
Control
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12. Guidelines For Identifying Classes
The followings are guidelines for selecting classes in your application:
Look for nouns and noun phrases in the problem statement
Some classes are implicit or taken from general knowledge
Eg:-HR management system
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13. Approaches for Identifying Classes…
Noun Phrase Approach
Common Class Pattern Approach
CRC(Classes, Relation, Collaboration) Approach
Use-Case Driven Approach--The unified approach uses the use-case driven approach for identifying classes and understanding behaviour of objects.
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14. Module VII Object Analysis:Classification
Noun Phrase Approach
Using Noun Phrase method, you have to read through the use cases or requirements.
One way of gathering requirements is through interviews.
Change all plurals to singular and make a list, which can then be divided into three categories
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15. Module VII Object Analysis:Classification
Noun Phrase Approach
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16. Noun Phrase Approach… Irrelevant classes are simply scraped off.
You must be able to formulate a statement of purpose for each candidate class; if not, simply eliminate it.
Flexibility is a virtue.
Flexible bcoz it is an incremental and iterative approach.
Redundant classes-part of common vocabulary. if mre than one word is being used to describe the same idea select the one that is most meaningful in context of the system.
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17. Module VII Object Analysis:Classification
Noun Phrase Approach…
Adjective Classes
Does the object represented by the noun behave differently when the adjective is applied to it ?
If use of adjective signals that behaviour of class is different then make a new class.
“Current Account Holder” “Savings Account holder”
Attribute Classes
Tentative objects used only as values should be defined or restated as attributes and not as a class.
Eg:- Client status.
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18. Guidelines For Refining Classes
Redundant Classes:
Do not keep two classes that express the same information.
If more than one word is being used to describe the same idea, select the one that is the most meaningful in the context of the system.
Remember by FRIAR
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19. Common Class Patterns Approach…
Based on knowledge base of common classes that have been proposed by various researchers.
Events Class
An order, landing etc.
Organisation Class
Finance Department , HR Department.
People Class—those representing user of system and about whom info is kept in the system.
Eg-HR manager of a company is user of the employee management system and being an employee is also a part of the employee management system.
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20. Common Class Patterns Approach
Places-physical locations that system must keep info abt.
Offices, buildings
Tangible things and devices with which application interacts
Cars-tangible things, pressure sensors-devices.
Concepts
It is Principles or Ideas, for example Performance can be a concept class.
Remember by COPPET
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21. Module VII Object Analysis:Classification
CRC approach
Identify classes’ responsibilities(attributes and methods) and related classes that interact together
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22. Module VII Object Analysis:Classification
Continued…
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23. Module VII Object Analysis:Classification
Finding Structures
Subclass Hierarchies
Aggregations
Component-Assembly
Container-Contents
Collection-Member
Association
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24. Superclass-Subclass Relationsh
Top-down approach
Bottom-up approach
Reusability approach
(more details later at OOD)
Multiple inheritance approach
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25. Module VII Object Analysis:Classification
Aggregation
A relationship between two classes where the instances of one class are in some way components, members, or contents of the instances of the other class
Appear on the class diagram along with all the subclass hierarchies and the regular associations
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26. Module VII Object Analysis:Classification
Aggregation
3 relationships that sometimes occur in an object model
Whole-Part or Component-Assembly
Container-Contents
Collection-Member
Improve communication and understanding
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27. Module VII Object Analysis:Classification
Component-Assembly
Constructed from its parts and an assembly-part situation physically exists
A product and it’s components
French soup consists of onion, butter, flour, wine, French bread, cheddar cheese, etc.
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28. Module VII Object Analysis:Classification
Container
A physical whole encompasses but is not constructed from physical parts
A house can be considered a container for furniture and appliances
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29. Module VII Object Analysis:Classification
Collection-Member
A conceptual whole encompasses parts that may be physical or conceptual
Teachers are assigned to specific courses
A football team is a collection of players
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30. Aggregation – 2 extra features
Transitivity
If A is part of B and B is part of C, then A is part of C
For example, a timing belt is part of an engine and an engine is part of a car; therefore, a timing belt is part of a car
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31. Aggregation – 2 extra features...
Antisymmetry
If A is part of B, then B is not part of A
For example, an engine is part of a car, but a car is not part of an engine
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32. Module VII Object Analysis:Classification
A filled diamond signifies the strong form of aggregation, e.g. assembly-component
“Weak” forms of aggregation might be represented using a hollow diamond , e.g. Container and Collection
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33. Module VII Object Analysis:Classification
Associations
Location: next To, part of, contained in, ingredient of etc.
cheese is an ingredient of French soup
Communication: to, order to…
a customer places an order with an operator
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34. Module VII Object Analysis:Classification
Associations...
Implementation: Defer implementation-specific associations to the design phase
Ternary: Ternary or n-ary association is an association among more than two classes
Directed actions (derived): can be defined in terms of other associations
avoid these types of association - redundant
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35. MODULE-IV OO Methodologies
ViaNet Bank ATM System
The bank client must be able to deposit an amount to and withdraw an amount from his/her account using the touch screen at the ViaNet Bank ATM kiosk.
Each transaction must be recorded, and the client must be able to review all transactions performed against a given account.
Recorded transactions must include the date, time, transaction type, amount, and account balance after the transaction.
No receipts will be provided for any account transactions.
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36. MODULE-IV OO Methodologies
ViaNet Bank ATM System...
The bank application operates for a single banking institution only.
For each checking account, one related savings account can exist. A checking account differs from other bank accounts in that it often allows for numerous withdrawals and unlimited deposits, whereas savings accounts sometimes limit both.
Access to the ViaNet accounts is provided by a PIN code consisting of 4 integer digits between 0 and 9.
One PIN code allows access to all accounts held by a bank client.
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37. MODULE-IV OO Methodologies
ViaNet Bank ATM System...
Neither a checking nor a savings account can have a negative balance.
The system should automatically withdraw money from a related savings account if the requested withdrawal amount on the checking account is more than the current balance.
If the balance on a savings account is less than the withdrawal amount requested, the transaction will stop and the bank client will be notified.
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38. The Noun Phase Approach
Account, Account Balance, Amount, Approval process, ATM Card, ATM Machine, Bank, Bank Client, Card, Cash, Check, Checking, Checking Account, Client, Envelope, Client’s Account, Currency, Dollar, (Four) Digits, Fund, (Invalid) PIN, Message, Money, Password, PIN, PIN Code, Record, Savings, Savings Account, Step, System, Transaction, Transaction History
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39. The Noun Phase Approach…
Irrelevant Classes
Envelope, Four Digits, Step
Redundant Classes
Client, Bank Client = BankClient
Account, Client’s Account = Account
PIN, PIN Code = PIN
Checking, Checking Account = CheckingAccount
Savings, Savings Account = SavingsAccount
Fund, Money = Fund
ATM Card, Card = ATM Card
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40. The Noun Phase Approach…
Adjective Classes
Not applicable
Attribute Classes
Amount
Account Balance
Invalid PIN
Password
Transaction History
PIN
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41. The Noun Phase Approach…
Statement of purpose
ATM Machine: an interface to the ViaNet Bank
ATM Card: a key to an account
BankClient: an individual with a checkings account and possibly a savings account.
Bank: clients belong to the bank
Account: defines behaviours of account types
CheckingAccount: withdrawal service
SavingsAccount: models a client’s savings
Transaction: keeps track of transaction data
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42. MODULE-IV OO Methodologies
Common Class Patterns
People
Bank Client
Places
Nothing applicable here.(Lets consider For eg: Bank Branch)
Tangible things and Devices
ATM Machine
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43. MODULE-IV OO Methodologies
Common Class Patterns...
Events
Account class, CheckingAccount(models a client’s checking account and provides more specialized withdrawal service), SavingsAccount, Transaction
Organisation Classes: Bank class
Concept Classes: N/A
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44. MODULE-IV OO Methodologies
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45. MODULE-IV OO Methodologies
Use Case Driven Approach: Identifying Classes And Behavior Through Sequence/Collaboration Modeling
Develop sequence diagram classes becomes clear.
The process of creating sequence or collaboration diagrams is a systematic way to think about how a use case (scenario) can take place; and
By doing so, it forces you to think about objects involved in your application.
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46. MODULE-IV OO Methodologies
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47. Guidelines for Naming Classes
The class name should be singular. Eg: YouthMember.
Use names with which the users or clients are comfortable. Eg WithdrawCash
Choose the class name from standard vocabulary for the subject matter.
The name of a class should reflect its intrinsic nature.
Use readable names with capitalize words. Ex: LoanWindow
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48. MODULE-IV OO Methodologies
CRC
CRC cards: Classes, Responsibilities And Collaborators
Developed by Cunningham, Wilkerson and Beck.
CRC is a technique for identifying classes’ responsibilities therefore their attributes and methods.
CRC helps in identifying classes.
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49. MODULE-IV OO Methodologies
CRC…
CRC cards are 4” x 6” index cards consisting of :
The class name
Its Super and Sub classes (if applicable)
The responsibilities of the class.
The names of other classes with which the class will collaborate to fulfill its responsibilities.
Author
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50. MODULE-IV OO Methodologies
CRC Layout
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51. MODULE-IV OO Methodologies
CRC Card Example
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52. MODULE-IV OO Methodologies
END of Chapter-7
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