1. Information system analysis and design
Dr. Dina Tbaishat

2. Recap
Last lecture we discussed some aspects of the system where design is necessary, such as database and interface
Today we shall look at Object Oriented design – applied in OO development
We have mentioned UML before when we discussed the use case diagram
Today we shall look at other UML tools that are used in the design phase, more specifically, when designing using objects

3. Basic concepts
Object Oriented (OO) programming uses a programming language that supports direct implementation of objects and identifies classes (such as Java)
“Object oriented design is concerned with developing an OO model of a software system to implement the identified requirements” (Sommerville, 2001)
Therefore, object oriented design is part of OO development

4. Objects and object classes
According to Sommerville (2001):
“An object is an entity that has a state and a defined set of operations which operate on that state. The state is represented as a set of object attributes. The operations associated with the object provide services to other objects“
“Objects are created according to an object class definition. An object class definition serves as a template for creating objects. It includes declarations of all the attributes and operations which should be associated with an object of that class”

5. An example of a class called “flight”:
An example of a class called “bank account”

6. Objects on the other hand have state and behaviour
Dogs have state (name, color) and behavior (barking…). Bicycles also have state (current speed) and behavior (applying brakes)
An object is an instance of a class
Classes allow inheritance, for example:

7. To design using OO, it is important to first understand and define the context of the system, define the objects, then develop a design model
UML provides large number of possible static and dynamic models that maybe used in the design phase, and also, be documented
Examples of UML design models are listed next:

8. (1) Sub system models which show the groupings of objects into sub systems, these are represented using “package diagram”
These are static models
Example of packages in a package diagram for registration process at a university: manage fees, enrollment, manage loans and grants
The notation for a package diagram is:

9. An example of a class diagram:

10. (2) Sequence models which show the sequence of object interactions
These are dynamic models
For example:

11. (3) State machine models which show how objects change their state
These are also dynamic
An example in UML is the state diagram:

12. Please read the paper about advantages and disadvantages of OO programming

13. Is UML enough?
UML is not a full list of all the diagrams you may need for analysis and design
If no UML diagram is appropriate, use a non UML diagram
Decision tables for example are good to show complicated logical conditions

14. References
Sommerville, I. (2001). Software Engineering. UK: Addison Wesley
Fowler, M. (2004). UML Distilled Third Edition: A Brief Guide to the Standard Object Modelling Language. UK: Addison Wesley
Diagrams examples are published on the internet