The following characteristics of Object Orientation had a positive impact on our case
study Sales Order system.
Re usability - A powerful feature of the OO is that the classes, Use Cases and objects
can be re used in the same or in a different application. The classes that we have used in
this system could be used in another similar system. This will minimise the amount of time
and labour in defining new entities.
Inheritance - Sales person, Customer and supplier inherit the attributes from the class
Person. Because of this characteristic it is not necessary to define attributes for each
of the classes i.e. Sales Person, Customer and supplier.
Aggregation - The class Date is used in component classes, Order class, Item Class and
Commission class. As examples, in Order Class the lead-time of the order can be
identified. In Commission class it will assist in calculating the correct commission for
the Sales Persons. In Item class it will assist to find out when an item is available for
despatch.
In Entity Relationship Diagrams you can not show Many to many (M:N) relationships. If
there are M:N relations, those have to be decomposed. But in OO you can show 1:1, 1:M and
as well as M:N relationships. Because of this feature the hazel of creation of
Joining tables is eliminated.
When implementing the system, OO Design is convenient for the developers since it
generates classes. This facility will assist the developers to generate code in a much
more organised way.
It is easier to understand the functionality of OO than SSD. In a DFD or ERD the users
have to visualise how the system is going to function. But in OO the functionality is
apparent since the performance of each element is clearly defined. As an example in a
class the objects are clearly connected to actions that they perform since a class
contains both data and procedures.
It is easy to add functionality. Since the Use Cases are uniquely defined for each of
the requirement, the developer will know exactly where and what to change without
affecting the system. This because you can always extend a class via inheritance, without
having to change the existing code.
From the point of view of the users, the Use Cases assist to understand the
functionality provided by the system better than the context diagram does, this makes it
easier for the user to check if all the requirements have been included. Also Uses Cases
will save time in implementation since they can be extended or re-used.
