Object oriented analysis questions for Computer Science and MCA students

What are the steps to be followed to create CRC models?

What is CRC models?
  • CRC model stands for Class Responsibility Collaborator Model.
  • It is a collection of standard index cards that have been divided into three sections:

    I. Class Name
    II. Responsibilities
    III. Collaborators
Class Name
Class NameCollaborators
  • A 'Class name' represents a collection of similar objects.
  • A 'Responsibility' is something that a class knows or does.
  • A 'Collaborator' is another class that a class interacts with to fulfill its responsibilities.
  • It is used in the design of object oriented software.
  • It is a collection of CRC cards that represent whole or part of an application or problem domain.
Steps to create CRC models

Following are the steps of CRC model:
1. Find Classes
2. Find Responsibilities
3. Define Collaborators
4. Define Use-Cases
5. Arrange the cards on the table

1. Find Classes
  • Look for anything that interacts with the system, or is a part of the system.
  • Look for reports generated by the system.
  • Look for any screens used in the system.
  • Immediately prototype interface and report classes.
  • Look for the three to five main classes right away.
  • Create a new card for a class immediately.
  • Use one or two words to describe the class.
  • Class names are singular.
2. Finding Responsibilities
  • Ask yourself what the class knows.
  • Ask yourself what the class does.
  • If you have identified a responsibility, ask yourself what class it "belongs" to?
  • Sometimes get responsibilities that we won’t implement, and that’s OK.
  • Classes will collaborate to fulfill many of their responsibilities.
3. Defining Collaborators
  • Collaboration occurs when a class needs information that it doesn’t have.
  • Collaboration occurs when a class needs to modify information that it doesn’t have.
  • There will always be at least one initiator of any given collaboration.
  • Sometimes the collaborator does the bulk of the work.
  • New responsibilities may be created to fulfill the collaboration.
4. Defining Use-Cases
  • The BDEs will identify them as the responsibilities of actor classes.
  • Transcribe the scenarios onto cards.
5. Arrange the cards on the table
  • Cards that collaborate with each other should be close to one another on the desk.
  • The more that two cards collaborate, the closer that they should be on the desk.
  • Expect to be moving the cards around a lot at the beginning.
  • Put "busy" cards towards the center of the table.
  • People will identify relationships/associations between classes as they move them around.
Advantages of CRC Models
  • It breaks down communication barriers.
  • It is simple and straightforward.
  • It is non-threatening to users.
  • It is inexpensive and portable.
Disadvantages of CRC Models
  • It is hard to get users together.
  • It is threatening to some developers.
  • Sometimes CRC cards are limited.

Write a short note on relation between sequence diagrams and use case diagram.

Relation between Sequence Diagrams and Use Case Diagram:
  • Use case diagrams show business use cases, actors and the relationships between them. The relationships between actors and business use cases, state than an actor can use a certain functionality of the business system.
  • A sequence diagram can map a scenario described by a use case in step by step detail to define how objects collaborate to achieve your application's goals.
  • A Use-Case model is built and the actors are connected to use cases. Each use case represents a task in which the actor participates.
  • For each use case, a sequence diagram is built. Each sequence diagram specifies the main interaction steps to be achieved for each use case.
  • Some of the interaction steps in a sequence diagram can be deployed in another sequence diagram.
  • From the sequence diagrams, use-case relationships are identified.
  • Sequence subdiagrams are identified with new use cases, then the inclusion relationships are identified between the use cases specified and the new use cases.
  • The sequence diagrams are refined. From the refined sequence diagrams, new use-case relationships are discovered.

Draw use case diagram for Online Railway Reservation System. Make necessary assumptions.

Use case diagram for Online Railway Reservation System:
online railway use case

Draw activity diagram for Online Transaction Management System (e-shopping). Make suitable assumptions.

activity diagram Online Transaction E-Shopping

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