DATA FLOW DIAGRAM (DFD)
Data flow diagram represents flow of data through system.
1. DFD is a graphic tool which defines input , output and processes of the system.
2. It helps analyst to explain his understanding of the system to user.
Symbols used:- Different symbols represent different system elements. But
use of symbol associated with each element depends upon which approach is used.
There two types of popular symbol ling styles.
Rules For Constructing Data Flow Diagrams
1. Procedures should be named and numbered for easy reference.
2. Process should be numbered if exploded into lower level.
3. Names of data sources, destination &stores should be in capital letters.
4. Process and data flow names should have first letter capital.
5. The direction of flow is from left to right and top to bottom. Traditional flow of data is
from source (upper left corner ) to the destination (lower right corner)
a) It contains and represents single process and determines the boundary of the
system.
b) Name of the process usually represents the name of the system.
c) All entities are shown at context level and should remain the same
(even the name )through all the level.
do’ s and dont’s in data flow diagram:
Dataflow should reflect the data not the documents on which it resides
Process name should fully describe the action taking place and should be able
to explain inflows & out flows of the data.
Avoid usage of vague names to the activity such as Review, Handle.
Assign unique process names to the activity.
Data stores should represent logical names indicating what kind of data is stored.
Don’t assign program specific names like STUDENT.DBF to document names.
No new entity or data store at any level which does not papers at a level
previous to that level.
No data flow should cross over through all the levels in the DFD.
Important guide lines for data stores and entities:
Data stores mainly are of two types
1. Master
2.Transaction.
Data store should have only related data stored in them.
All data stores appearing at the first level should also appear at lower levels.
Entities which get repeated right from context level to the lower levels are
shown by -
Data stores which are used to access stored data more than once are shown by
Data flows going onto a process and coming out of a process should have
different names
For example
Verify student’s details
Students –mast student details verified student’s details
Case Study: Draw context level, first level DFD for following system. A xyz company procures the material against the requisition received from stores. Purchase department prepares a purchase order and sends a copy of it to stores for ready reference. Stores department receives the material from the vendor and prepares GRN [goods receipt note].Stores department updates the stock of the items for the accepted quantity mentioned in GRN.
Solution : Context Level DFD
First Level DFD For Purchase Order System :
