Object Diagram In UML

An object diagram 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. 

Difference between class and object diagram

A class diagram may also contain interfaces, packages, relationships, and even instances, 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.

Purpose of Object Diagram

The use of object diagrams is fairly limited, mainly to show examples of data structures.

• During the analysis phase of a project, you might create a class diagram to describe the structure of a system and then create a set of object diagrams as test cases to verify the accuracy and completeness of the class diagram.
• Before you create a class diagram, you might create an object diagram to discover facts about specific model elements and their links, or to illustrate specific examples of the classifiers that are required.

Basic Object Diagram Symbols and Notations

Object Names: Every object is actually symbolized like a rectangle, that offers the name from the object and its class underlined as well as divided with a colon.
Object Attributes: Similar to classes, you are able to list object attributes inside a separate compartment. However, unlike classes, object attributes should have values assigned for them.
Links: Links tend to be instances associated with associations. You can draw a link while using the lines utilized in class diagrams.

Example:

The following diagram is an example of an object diagram. It represents the Order management system .The following diagram is an instance of the system at a particular time of purchase. It has the following objects.

·        Customer

·        Order

·        SpecialOrder

·        NormalOrder

Now the customer object (C) is associated with three order objects (O1, O2, and O3). These order objects are associated with special order and normal order objects (S1, S2, and N1). The customer has the following three orders with different numbers (45, 60 and 80) for the particular time considered.

The same is true for special order and normal order objects which have number of orders as 20, 30, and 60. If a different time of purchase is considered, then these values will change accordingly.