INTRODUCTION
 Data Flow diagrams graphically characterize data processes and flows in a business system.
 In their original state data flow diagrams depict the broadest possible overview of system inputs, processes and outputs, which correspond to those of the general systems model discussed.
 A series of layered data flow diagrams may also be used to represent and analyze detailed procedures within a larger system.

THE DATA FLOW APPROACH
 When systems analysts attempt to understand he information requirements of users, they must be able to
 conceptualize how data moves through the organization,
 the processes or transformation that the data undergoes
 what the outputs are
 The data flow approach emphasizes the logic underlying the system.
 By using combinations of only four symbols, the systems analyst can create a pictorial depiction of processes that will eventually provide solid system foundation.

ADVANTAGES OF USING DFD
1.
Freedom from committing to the technical implementation of the system too early.
2.
Further understanding of the interrelatedness of systems and subsystems.
3.
Communicating current system knowledge to users through data flow diagrams.
4.
Analysis of a proposed system to determine if the necessary data and processes have been defined.

CONVECTIONS USED IN DFD
 Four basic symbols are used to chart movement on data flow diagrams. They are:
 A Double Square
 An arrow
 A rectangle with rounded corners
 A rectangle
 An entire system and sub-system can be depicted graphically with these four symbols in combination.

CONVECTIONS USED IN DFD
4 BASIC SYMBOLS USED IN DFD
Entity
Student
Flow of data
Process
New Student
Information
2.1
Create
Student record
Data Store D3 Student Master

CONVECTIONS USED IN DFD
THE DOUBLE SQUARE
 This is used to depict an external entity (another department, a business, a person or a machine) that can send data to or receive data from the system.
 The external entity or entity, is also called a source or destination of data, and it is considered to be external to the system being described.
 Each entity is labeled with an appropriate name.

CONVECTIONS USED IN DFD
THE DOUBLE SQUARE
 Although it acts with the system it is considered as outside of the boundaries of the system.
 Entities should be named with a noun.
 The same entity may be used more than once on the same data flow diagram, to avoid crossing data flow line.

CONVECTIONS USED IN DFD
 The arrow shows movements of data from one point to another, with the head of the arrow pointing towards the data’s destination.
 Data flows occurring simultaneously can be depicted doing just that through the use of parallel arrows.
 Since an arrow represents data about a person, place or thing, it should be described with a noun.

CONVECTIONS USED IN DFD
THE RECTANGLE WITH ROUNDED CORNERS
 This is used to show the occurrence of a transformation process.
 Processes always denote a change in or transformation of data; hence, the data leaving a process is always labeled differently from the one entering it.
 Processes represents work being performed within the system and should be named using one of the following formats.

CONVECTIONS USED IN DFD
THE RECTANGLE WITH ROUNDED CORNERS
 A clear name makes it easier to understand what the process is accomplishing.
 Assign the name of the whole system when naming a high-level process (Context Level Diagram). eg.
INVENTORY CONTROL SYSTEM.
 The name of a sub-system, use a name such as
INVENTORY REPORTING SUBSYTEM.

CONVECTIONS USED IN DFD
THE RECTANGLE
 These symbols are drawn only wide enough to allow identifying lettering in the rectangle.
 In logical data flow diagrams, the type of physical storage (e.g., tape, diskette, cd) is not specified.
 At this point the data store symbol is simply showing a depository that allows addition and retrieval of data
 The data store may represent a manual store, such as a filing cabinet, or a computerized file or database.

CONVECTIONS USED IN DFD
THE RECTANGLE
 Since data store represent a person, place, or thing they are named with a noun.
 Temporary data stores, such as scratch paper or a temporary computer file, are not included on the DFD.
 Give each data store a unique reference number, such as, D1, D2, D3, and so on, to identify it level.

1
RULES FOR DRAWING DATA
FLOW DIAGRAMS
2
Data Flow should not split into two or more different data flows.
3

RULES FOR DRAWING DATA
FLOW DIAGRAMS
All data flows must
EITHER originate or terminate at a process

RULES FOR DRAWING DATA
FLOW DIAGRAMS
Processes needs to have at least one input data flow and one output data flow

CREATING THE CONTEXT
DIAGRAM
• This is an overview, one including basic inputs,
The general system and outputs.
• This will be the most general diagram – really, a bird’s-eye view of data movement in the system and the broadest possible conceptualization of the system.
• The context diagram is the highest level in a dat flow diagram and contains only one process, representing the entire system.

CREATING THE CONTEXT
DIAGRAM
• The process is given the number 0.
• All external entities are shown on the contest diagram, as well as major data flow to and from them.
• The diagram does not contain any data stores and is fairly simple to create, once the external entities and the data flow to and from them are known to analysts from interviews with users and as a result to document analysis.

CREATING THE CONTEXT
DIAGRAM
Entity
1
Input A
0
System Name
Output C
Entity
3
Entity
2
Input B

A supermarket uses a Point of Sale (POS) terminal to keep track of the goods that is in stock and to produce bills for customers. Whenever an item is sold, the product code of the item is read by a barcode scanner. The price and name of the product is checked in the supermarket’s stock database and this information is printed on the customer’s receipt. It also updates the product’s record in the stock file to indicate that the product has been sold.
Draw a context level diagram using the information above.