Summary

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A class embodies a set of responsibilities that define the behavior of the objects in the class. The responsibilities are carried out by the operations defined for the class. The structure of an object is described by the attributes of the class. Each attribute is a data definition held by objects of the class. Objects defined for the class have a value for every attribute of the class. The attributes and operations defined for a class are the ones that have meaning and utility within the application that is being developed.

Messages in interaction diagrams typically are mapped to operations of the receiving class. However, there are some special cases where the message does not become an operation: messages to and from actors representing people and messages to and from classes representing GUI classes.

Many of the attributes of a class are found in the problem statement, the set of system requirements, and the flow of events documentation. They may also be discovered when supplying the definition of a class. Finally, domain expertise is also a good source of attributes for a class.

A relationship may also have structure and behavior. This is true when the information deals with a link between two objects and not with one object by itself. The structure and behavior belonging to a relationships is held in an association class.

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