Com S 362: Object-Oriented Analysis and Design Class, Responsibilities, Collaborations, CRC Cards...

Com S 362: Object-Oriented Analysis and Design

Class, Responsibilities, Collaborations, CRC Cards


Oct 18, 2006


From Analysis to Design

• Input artifacts: use cases, domain model, system sequence diagrams

• Refine these artifacts, one step closer to the executable system


Key Steps

• Finding entities in your system– These entities will become classes

• Assigning responsibilities to these classes– Often become operations that a class support

• Identifying collaborations between classes– Represent relationships between classes– Often describe dependence


Relation to Previous Phases

Analysis: Domain Model

• Identify conceptual classes

• Identify attributes of conceptual classes

• Identify association between conceptual classes

Design: Class Diagrams

• Identify solution classes

• Identify responsibilities of solution classes

• Identify collaboration between solution classes


Finding Solution Classes

• Conceptual Classes in Domain Model– Not every conceptual class may be required– Example: Copyright law, a conceptual class, but

may not be a solution class– Some conceptual classes may become attributes– Example: Library, a conceptual class, but may

just be an attribute, if only name is useful

• Use cases


Example: Domain Model

Initial Class List: Patron, Book, Fine, Librarian,

Manager, Library, Partner Library


Refining Class List: Redundancy

• Initial class list: patron, book, fine, librarian, manager, library, partner library

• Question: Are all user types (patron, librarian, manager) necessary?



• Alternative: can we have a generic user type with different permissions for patrons, librarians, and managers?

• Refined class list : user, permissions, book, fine, library, partner library



• Alternative rejected: Coupling between different user types in one class

• Change in any user type’s behavior affects this class

• Refined class list : patron, book, fine, librarian, manager, library, partner library

• Low coupling [Larman page 299-301]


Refining Class List: Relations


• Question: Are patrons, librarians, managers related?


Refining Class List: Relations

• Alternative: Can we have another class user, the patrons, librarians, managers are all users at some level?

• Refined class list : user, patron, book, fine, librarian, manager, library, partner library


Refining Class List: Attribute or Class


• Question: Is fine a property of a patron? Can fines exist by themselves?


Refining Class List: Attribute or Class

• Alternative: Can we have fines as an attribute of patrons?

• Refined class list : patron, book, librarian, manager, library, partner library


Refining Class List: Discovery


• Question: Does library owns items other than books?


Refining Class List: Discovery

• Alternative: Can we have another set of classes videos, CDs, DVDs?

• Refined class list: patron, book, videos, CDs, DVDs, fine, librarian, manager, library, partner library


Refining Class List: 1st Change

• Initial class list: patron, book, videos, CDs, DVDs, fine, librarian, manager, library, partner library

• Question: Is library ever going to own anything that we have not thought about here?


Refining Class List: 1st Change

• Alternative: Can we have another type Item, an abstraction of books, videos, CDs, DVDs?

• Refined class list: patron, Item, book, videos, CDs, DVDs, fine, librarian, manager, library, partner library


Refining Class List: 2nd Change

• Initial class list: patron, Item, book, videos, CDs, DVDs, fine, librarian, manager, library, partner library

• Question: Is library ever going to support multiple level of memberships? e.g, platinum can borrow unlimited, gold can borrow 25 items, silver can borrow 5 items, bronze can borrow 1 item only


Refining Class List: 2nd Change

• Alternative: Can we have another type IPatron, an abstraction of different type of patrons?

• Refined class list: IPatron, patron, Item, book, videos, CDs, DVDs, fine, librarian, manager, library, partner library


Refining Class List: 3rd Change

• Initial class list: IPatron, patron, Item, book, videos, CDs, DVDs, fine, librarian, manager, library, partner library

• Question: Is library ever going to support different type of librarians with different job responsibilities? Some will work at circulation desk, other kind at the reference desk, yet another kind are allowed to modify the library catalog and add new books.


Refining Class List: 3rd Change

• Alternative: Can we have another type ILibrarian, an abstraction of different type of librarians?

• Refined class list: IPatron, patron, Item, book, videos, CDs, DVDs, fine, ILibrarian, librarian, manager, library, partner library


Assign Responsibilities

• Where do responsibilities come from?– Use case scenarios– Objective is to fulfill user’s goals


Example Scenario• Success Scenarios #1: A patron approaches the

library administration machine with books to borrow. The patron enters her/his membership information. The machine verifies the membership information. The patrons enters the book information. The machine updates the library catalog to reflect that the book is checked out. The machine outputs a receipt containing the due date. The patron receives a receipt from the machine.

• Responsibilities are underlined


Identified Responsibilities • Prompt and store membership information

• Verify membership information

• Prompt and store book information

• Update the library catalog

• Output a receipt {Due date}

• Class list: IPatron, patron, Item, book, videos, CDs, DVDs, fine, ILibrarian, librarian, manager, library, partner library


Prompt and Record Member Info • Do we need to refine class list?

– How to prompt? – How to store?

• Class list: IPatron, patron, Item, book, videos, CDs, DVDs, fine, ILibrarian, librarian, manager, library, partner library


Classic case for 3-tiered architecture

User Interface

IPatron, patron, Item, book, videos, CDs, DVDs, fine, ILibrarian, librarian, manager, library,

partner library

Database


Information Expert• Which class has the necessary information

to prompt?

• Which class has the necessary information to store?

• Class list: IPatron, patron, Item, book, videos, CDs, DVDs, fine, ILibrarian, librarian, manager, library, partner library, User Interface, Database


Assigning Responsibilities

Class Name: UISubclasses: Super classes:

Responsibilities CollaboratorsPrompt IPatron

Class Name: IPatronSubclasses: PatronSuper classes:

Responsibilities CollaboratorsStore


Summary

• Identifying Solution Classes– Based on domain models– Based on use cases

• Refining Solution Class List

• Assigning Responsibilities to Classes

Com S 362: Object-Oriented Analysis and Design Class, Responsibilities, Collaborations, CRC Cards...

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