Data flow diagram were proposed by Larry Constantine.

In 1970s DFD became a popular way to visualize the major steps and data involved in Software System Processes.

It is a graphical representation of data flow.

It shows the processing steps as data flows through the system.

It shows end to end processing of data.

It takes input - process – output view of the system.

It plays important roll while developing the project.

DATA FLOW: it shows movement of data flows origin to destination

PROCESS: People , Procedures or devices that use data.

Entity: source of data or Destination of data which may be people , program interact with the system but are outside its boundary.

Data Store: Information that is kept and accessed. May be in paper file folder or a database . It may be exploded into various levels namely level 0 ,level 1 , level 3 etc.

PayrollProcessing

System

Departments

HumanResources

Govt.Agencies

Employees

Bank

Manage-ment

Employee checks

1.0UpdateEmpl.

PayrollFile

2.0Pay

Employ-ees

5.0Update

Gen.Ledger

4.0Pay

Taxes

3.0PrepareReports

Employee/Payroll File

GeneralLedger

HumanResources

Depart-ments Employees

Bank

Govt.Agencies

Manage-ment

Employeechange

form

New employeeform

Timecards

Employeepaychecks

Payrollcheck

Payrolldisburse-ment data

Payroll taxdisb. voucher

Tax report& payment

Payrollreport

A minimum of one data flow in and one data flow out of a process

A data store must be connected to a process(either in, out, or both)

An external entity must be connected to a process (either in, out, or both)

A single data flow must only flow one way

Process has no data flowing into it, but has data flowing out.

Data store is hooked to external entity. This means external entity can read and write to your data file without auditing!!

The data flow goes in two directions at once. Two or more arrows should be used to show the flow to and from each process.

They shows the flow of data through the system.

It shows process of i/o data.

It is also called as Bubble chart.

DFD supports a top – down approach for analysis

A state is a mode or condition of being.

A state diagram is a dynamic model showing changes of state that an object goes through during its lifetime in response to events.

State diagram depict the dynamic behavior of the system in response to external and internal events.

Initial state : It is a starting point or first activity of diagram. This is also known as “pseudo state” where the state has no variables and no activity.

Final state : It is the end of the state diagram. This is also a pseudo state because it does not have any variables or action described. A state diagram can have zero or more final states.

State : state is a recognizable situation and exists over an interval of time. This is denoted by a rounded rectangle and compartments within to describe state-name, variable and activity.

or

State-name

Variable

Activity

Transition : A transition is a change from one state to other is indicated by an arrow. The event and action causing the transition are written beside the arrow, separated by a slash.

Event and Action: A trigger that causes a transition to occur and changes the state is called as an event or action. An event occurs at a particular time has no duration.

Signal : when an event causes a message/trigger to be sent to a state, that causes the transitions; then, that message sent by the event is called as a signal. This is represented as <<Signal>> icon above the action/event.

Event [condition]/Action

<<signal>>Event/ Action

Event /Action

Enter Admin

Login

Invalid ID or

Password

<<Main menu page>>

Do: uploading , editing

personal details , sending

messages etc.

<<Check>>

Do: Admin Login

Try again

Yes No

User want to Stop

Valid ID and

PasswordSelecting

activities <<upload file>>

Do: choose file

<<Personal info>>

Do: change password ,

change E-mail id , change

details etc.

<<send msg>>

Do: sending message

If

select

editing

person

al

detail

If select

sending

messages

If select uploading

User want to Cancel

User want to Cancel

User want to Cancel

Waiting

for

upload

file

State chart diagram is used to represent the event driven state change of a system. It basically describes the state change of a class, interface etc.

State chart diagram is used to visualize the reaction of a system by internal/external factors.

State diagram (also called state chart diagrams) are used to help the developer better understand any complex functionality of specialized areas of the system.