Object Model. An object model is a representation of how object types fit into the business domain relative to other object types. The object model also shows the three types of properties for each object type: its associations, attributes, and methods.
The focus of an object model diagram may be the business domain. However, this can become unwieldy for a business domain of typical size (40 - 80 object types). Typically, the business domain is represented on the object model in categorized topics of 10 - 15 object types each.