Sunday, June 2, 2013

What is a UML Object Diagram?

Object diagrams are also closely linked to class diagrams. Just as an object is an instance of a class, an object diagram could be viewed as an instance of a class diagram. Object diagrams describe the static structure of a system at a particular time and they are used to test the accuracy of class diagrams.

Basic Object Diagram Symbols and Notations

Object names

Each object is represented as a rectangle, which contains the name of the object and its class underlined and separated by a colon.

Object attributes

As with classes, you can list object attributes in a separate compartment. However, unlike classes, object attributes must have values assigned to them.
Object attributes

Active object

Objects that control action flow are called active objects. Illustrate these objects with a thicker border.
Active object

Multiplicity

You can illustrate multiple objects as one symbol if the attributes of the individual objects are not important.
Multiplicity

Links

Links are instances of associations. You can draw a link using the lines used in class diagrams.
Links

Self-linked

Objects that fulfill more than one role can be self-linked. For example, if Mark, an administrative assistant, also fulfilled the role of a marketing assistant, and the two positions are linked, Mark's instance of the two classes will be self-linked.
Self-linked

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