Introduction to Class-Responsibility-Collaborator (CRC) Modeling

Class-responsibility-collaborator (CRC) modeling is a means to identify and organize classes relevant to system requirements. CRC model is a collection of index cards and it consists of three parts:

Classes : It is a collection of similar objects.
- Entity classes or business classes are obtained directly from statement of the problem. The information contained in these classes are important to users but they do not display themselves.
- Boundary classes are used to create interface which user sees and interacts with as software is used.
- Controller classes are designed to manage creation or update of entity objects, instantiation of boundary objects, communication between objects and validation of data.

Responsibility : something that a class knows or does. Some guidelines that can be applied for allocating responsibilities to classes are:
- System intelligence should be distributed across classes to best address the needs of the problem.
- Each responsibility should be stated as generally as possible.
- Information and the behavior related to it should reside within the same class.
- Information about one thing should be localized with a single class not distributed across multiple classes.
- Responsibilities should be shared among related classes when appropriate.

Collaborator : another class that the class interacts with to fulfill the responsibilities.
- It takes one of two forms : a request for information or a request to do something.
- If a class cannot fulfill all of its obligations itself, then a collaboration is required.
- Collaboration identifies relationship between classes.