Difference between Object Model Diagram and Class Diagram in Rational Rhapsody

Answer

Class diagram is a graph of classifier elements connected by their various static relationships. A “class” diagram may also contain interfaces, packages, relationships, and even instances,
such as objects and links. Perhaps a better name would be “static structural diagram”, but “class diagram” is shorter and well established.

Object diagram on the other hand is a graph of instances, including objects and data values. A static object diagram is an instance of a class diagram. It shows a snapshot of the detailed state of a system at a point in time. The use of object diagrams is fairly limited, mainly to show examples of data structures.

The actual differences lie in their purpose. A Class diagram shows your classes and their relationships. An Object Model Diagram shows the interaction between objects at some point, during run time.

A Class Diagram will show what the Objects in your system consist of (members) and what they are capable of doing (methods) mostly static. In contrast, an Object Diagram will show how objects in your system are interacting with each other at some point in time, and what values those objects contain when the program is in this state.