In Software Industry, there are two approaches to system modeling.

1) Traditional Approach

2) Object Oriented Approach

Traditional Approach: In the traditional approach, the system is viewed as a collection of processes. These processes interact with the outside world and with data elements. Processes accept inputs and can produce outputs. For a more detailed approach on the understanding of the traditional approach, please look for DFD, Entity-Relationship diagrams and Finite State Machines.

Traditional Approach can be broken up into the following:

1) Process Functional or DFD diagrams. Provides a graphical view of whats happening.

2) Entity Relationship Diagrams: Describes entities and relationship that exists between entities.

3) Behavior/Finite State Machines: Describes behavioral sequences of actions.

Object Oriented: In the object oriented world, a system is viewed as an object, or as a collection of objects. Objects interact with each other and with the outside world.

An example of a use case for a person withdrawing money from an ATM machine.

Name: Withdrawal

Actors: Customer, Keyboard, Display, Server, Card Reader, Cash Dispenser.

Pre-Condition: The customer has already inserted the card in the card reader.

Description: The following steps events portray the withdrawal use case:

a) System validates whether the card has not expired and is not stolen

b) The customer enters the pin in the system

c) The system validates the Pin number

d) If the Pin number is valid, the customer is presented with the menu on the display screen

e) Through the keyboard, the customer selects an account to withdraw money from

f) The system checks whether the

user account has sufficient funds to withdraw

the system has sufficient funds

the user has not exceeded his daily limit withdrawal

g) system performs withdrawl

h) cash dispenser has the money

i) printer receipt prints the receipt