Object Model 

The object model provides two resources: the class
diagram and the object diagram. The two diagrams
represent the resources of the problem domain that
the users would require even if the system were not
automated. The class diagram (often called the object
model) is the primary model. The class diagram
generates the code and provides the best definition
for the persistent objects of the system--the objects
that must be managed in a database. The object
diagram is a tool for testing and understanding the
objects that are represented by classes in the class
diagram.

The object model defines the resources of the
problem domain. These resources are the information
that the system must manage in order to support the
use cases. The use cases may create or alter the
resources, or simply access the information that the
objects own. Consequently, the object model is
partitioned to coincide with the functional partitions.