An object diagram is a snapshot of the objects in a system at a point in time. We can use an object diagram to show an example configuration of a snapshot from a class diagram. The figure shows the Class Diagram of Party Composition Structure and a particular snapshot at a point in time.
The object of the names are underlined and each name takes the form object name : class name. Both parts of the name are optional, so Robert and :Person are legal names. You can then show values for attributes and links in the object diagram and you can also think of an object diagram as a collaboration diagram without messages.