a bit similar to class diagrams, but it shows instances rather than classes

a diagram that shows a set of object s and the relationship s among them at a particular point in time

a graph of instances, including objects and data values

a graph whose nodes are object classes and whose arcs are relationship among classes

a snapshot of the objects in a system at a point in time

A diagram that encompasses objects and their relationships at a point in time. An object diagram may be considered a special case of a class diagram or a collaboration diagram. See: class diagram, collaboration diagram.

In the Unified Modeling Language (UML), an object diagram is a diagram that shows a complete or partial view of the structure of a modeled system at a specific time. This snapshot focuses on some particular set of object instances and attributes, and the links between the instances. A correlated set of object diagrams provides insight into how an arbitrary view of a system is expected to evolve over time.