UML

Uml class, object diagrams

Uml class, object diagrams

Overview

Object diagrams are derived from class diagrams so object diagrams are dependent upon class diagrams.

Object diagrams represent an instance of a class diagram. The basic concepts are similar for class diagrams and object diagrams. Object diagrams also represent the static view of a system but this static view is a snapshot of the system at a particular moment.

Object diagrams are used to render a set of objects and their relationships as an instance.

Purpose

The purpose of a diagram should be understood clearly to implement it practically. The purposes of object diagrams are similar to class diagrams.

The difference is that a class diagram represents an abstract model consists of classes and their relationships. But an object diagram represents an instance at a particular moment which is concrete in nature(Booch, et al., 2006).

It means the object diagram is more close to the actual system behaviour. The purpose is to capture the static view of a system at a particular moment. So the purpose of the object diagram can be summarized as:

* Forward and reverse engineering.

* Object relationships of a system

* Static view of an interaction.

* Understand object behaviour and their relationship from practical perspective

How to draw Object Diagram?

We have already discussed that an object diagram is an instance of a class diagram. It implies that an object diagram consists of instances of things used in a class diagram.

So both diagrams are made of same basic elements but in different form. In class diagram elements are in abstract form to represent the blue print and in object diagram the elements are in concrete form to represent the real world object.

To capture a particular system, numbers of class diagrams are limited. But if we consider object diagrams then we can have unlimited number of instances which are unique in nature(Alhir, 2008). So only those instances are considered which are having impact on the system.

From the above discussion it is clear that a single object diagram cannot capture all the necessary instances or rather cannot specify all objects of a system. So the solution is:

* First, analyze the system and decide which instances are having important data and association.

* Second, consider only those instances which will cover the functionality.

* Third, make some optimization as the numbers of instances are unlimited.

Before drawing an object diagrams the following things should be remembered and understood clearly:

* Object diagrams are consist of objects.

* The link in object diagram is used to connect objects.

* Objects and links are the two elements used to construct an object diagram.

Now after this the following things are to be decided before starting the construction of the diagram:

* The object diagram should have a meaningful name to indicate its purpose.

* The most important elements are to be identified.

* The association among objects should be clarified.

* Values of different elements need to be captured to include in the object ...