1

Session

Object Diagram

Checklist

Introduction to Object diagram

Explain Object diagram notations

Construct Object diagram for Case Study

2

Object Diagram

Object Diagram is snapshots of objects in the system at a particular point of time. Since objects

are also known as instances it is also known as instance diagram. Object diagram are useful to

test the correctness of class diagram.

Elements of an Object Diagram

There are only two elements in an object diagram – objects and links.

Objects

Objects are represented with compartments same as classes. Objects have only two

compartments name compartment and attributes compartment. Operator compartment is not

present in object diagrams because when there are more instances for an object you will be

seeing same operators for each instance. Syntax for Object name is as follows

All the parts of Objects are optional, Object name can also be “:Order” – this is known as

anonymous object. Each object should have value for its attributes.

Figure 1: Object Notation

Object name: class name

3

Link

Objects are connected with links (a line) that has names and no multiplicity. All links are one to

one and roles can be attached to links. In the below example OrderId_5 is an instance of Order

class and has produced two products [anonymous object & Vendor_Id_112]. Customer and

Vendor are role names that are denoted on the links.

Figure 2: Link Notation

Testing Order processing system with Object diagram

Let us consider our last constructed class diagram and test the object of Order.

Figure 3: Object Diagram - Order Processing System v0.1

4

There are certain errors with our order object. They are as follows

1. It seems order number and bill numbers are duplicating each other. It is sufficient to

have one of them.

2. I have specified the type of orderDetails as String

but it would be better to create an object for it,

since we would need multiple details like Product

Name, Weight, Unit Price, Any discount applicable

for the product.

3. I have mentioned type of lineItem as ArrayList but

in the interface add operator’s attribute is

LineItem which is incorrect

Based on the above object diagram we were able to detect some of the flaws. I have

redesigned the class diagram. The update Order Processing System class diagram is shown

in Figure 5. Updated Object diagram is present below.

Figure 5: Object Diagram v0.2

Figure 4: Interface with Error

5

Figure 6: Class Diagram - Order Processing System v0

6

Review

Object diagram represent snapshots of object at a particular

time

Object diagram is also known as instance diagram

Elements of object diagram – Objects and links

We have deducted flaws for our class diagram and corrected

them