In the first week of class you worked on a design for an elevator. In subsequent problems and labs, you have been given a specification for a class in terms of its behavior and responsibilities and have been asked to implement the class. This activity is often referred to as prototyping rather than designing. Today, we will return to the issue of actual design.

Given a general problem statement, what are the classes? What are the responsibilities and behavior of each class? What classes interact and how should that interaction be structured? Design is an iterative process and the roles of classes often change as the designers elaborate the requirements and work through scenarios (use cases) of how the system will be used. Because of the complexity of the interactions, design is usually a group activity.

• CRC stands for Class, Responsibility, and Collaborators.
• For any one class, the responsibilities are the member functions associated with the class and the collaborators are classes that interact with the class.
• All are listed on one index card.
• The design process consists of defining object behavior (methods) and interaction.

• As you talk about the problem, you will need to identify classes that participate and their behavior. One way of thinking about it is that nouns either correspond to classes or to data fields within classes, while verbs correspond to methods.
• Write down the nouns and verbs you use as you talk about the problem in two different columns on a piece of paper. As you start to see relationships, you will transfer the information to the CRC cards.
• When you identify a class that will be needed, designate a group member to be responsible for that class.
• The responsible person will make a CRC card for that class. That person will hold and maintain the CRC card as the design progresses.
• At the end of the class period, put the group number on each card and hand in your notes and cards with the names of your group members.

You have been asked to implement a course registration system for TuHard University, your alma mater. The system keeps track of all of the students enrolled at the University. It also keeps track of the class lists and other relevant information about the courses.

To help you get started, begin with two classes --- one class representing a single student and another class representing a single course. Work through the interactions between a single student and a single course during the registration process. What does a student do? What does the course do? These are the responsibilities of these classes. In the process of design, you will specify other classes and how they interact.

The information on a CRC card is supposed to fit on a 3x5 card. This is to prevent the design of complex classes with too many responsibilities.