Explain Class-Responsibility-Collaborator (CRC) Modeling and data modeling with an example.

4.A] Explain Class-Responsibility-Collaborator (CRC) Modeling and data modeling with an example.

Answer:

Class-Responsibility-Collaborator (CRC) Modeling

Class-Responsibility-Collaborator (CRC) modeling is a technique used to identify and organize the classes, their responsibilities, and their collaborations within a system. It is especially useful in object-oriented design. Here’s how CRC modeling works:

Components of CRC Modeling:

1. Class: The name of the class being modeled.
2. Responsibilities: The attributes and operations that the class must handle. Responsibilities define what the class knows and what it can do.
3. Collaborators: Other classes that the class interacts with to fulfill its responsibilities. Collaborators provide the information or functionality required by the class.

How to Create a CRC Model:

• Index Cards: Each class is represented by an index card. On the card:
• Top Section: Name of the class.
• Middle Section: List of responsibilities (what the class does or knows).
• Bottom Section: List of collaborators (other classes that help the class fulfill its responsibilities).

Example: SafeHome System

Imagine developing a SafeHome security system. Here’s a simplified CRC model:

CRC Index Card for FloorPlan Class:

• Class: FloorPlan
• Responsibilities:
• Defines floor plan name/type
• Manages floor plan positioning
• Scales floor plan for display
• Collaborators:
• Wall (for managing walls)
• Camera (for displaying camera views)

CRC Index Card for Camera Class:

• Class: Camera
• Responsibilities:
• Determines camera type
• Translates camera location
• Displays camera view
• Collaborators:
• FloorPlan (for determining camera position on the floor plan)

Data Modeling

Data Modeling involves defining and structuring data objects and their relationships within a system. It typically includes creating Entity-Relationship Diagrams (ERDs) to visualize data structures.

Components of Data Modeling:

1. Data Objects: Represent composite pieces of information with attributes. Examples include entities like Person and Car.
2. Attributes: Properties of data objects. For example, a Car might have attributes like Make, Model, Color, and Owner.
3. Relationships: Define how data objects interact or relate to each other.

How to Create a Data Model:

• Identify Data Objects: Determine the key entities or objects in the system.
• Define Attributes: Specify the properties for each data object.
• Establish Relationships: Define how different data objects are related to each other.

Example: Car Ownership System

Consider a system that manages car ownership:

Entity-Relationship Diagram:

• Data Object: Person
• Attributes: Name, Driver’s License Number
• Data Object: Car
• Attributes: Make, Model, ID Number, Color
• Relationships:
• A Person owns a Car.
• A Person is insured to drive a Car.

ER Diagram:

[Person] ----- (owns) ----- [Car]

In this diagram:

• Person and Car are entities.
• owns is a relationship indicating that a person can own a car.

Summary:

• CRC Modeling helps in organizing classes by defining their responsibilities and collaborations, using index cards to visualize the interactions.
• Data Modeling focuses on defining and structuring data objects and their relationships, often visualized through ER diagrams to illustrate how different pieces of data interact.

Both techniques are essential for designing robust software systems by ensuring that responsibilities are well-distributed and data is accurately represented and interconnected.