INTRODUCTION TO DATA FLOW DIAGRAMS
Data flow diagrams are part of a structured model in the development
of software. Data flow diagrams are a graphical technique that depicts
information flow and the transforms that are applied as data move from
input to output.
Basically, the function of Data Flow Diagrams is to show the user a graphical
analysis of a software system. It is kind of like a flowchart, except Data
Flow Diagrams show the flow of data throughout the system.
The chart below shows the basic notation of the Data Flow Diagrams.
Basic Data Flow Notation
| 1) Rectangle (external entity) - a producer or consumer of information that resides outisde the bounds of the system to be modeled |  |
| 2) Circle (process) - a transformer of information that resides within the bounds of the system to be modeled |  |
| 3) Line with an arrow ( data item) - a single item, or a collenction of data items. Arrow head represents the direction of the data |  |
| 4) Two parrallel lines (data srore) - a repository of data that is to be stored for use by one or more processes; may be as simple as a buffer or a queue or as sophisticated as a relational data base |  |
Data Flow Diagrams are also broken up into levels. You begin with a Level
0 (which is the general software system) The example below shows a simple
example of a Level 0 Data Flow Diagram. Based on how many inputs and outputs
(processes or number of circles) a system may have will determine how many
levels a user will have to go to get a detailed enough design of the software
system. Normally, a designer will go three levels deep in the Data Flow
Design.
Simple example of a Data Flow Diagram
This example is a basic Level 0 of a Data flow Diagram. As you can see
from the picture the rectangles represent external entities. These could
include a password, or code a user would have to enter. The external entities
relate to the main process of the system. basically they give the inputs
of the system. At Level 0 no details about the system are given, just inputs
and outputs. The system then gives output information to the client or
to the printer. From here the system would be broken down further and more
specifically in Levels 1,2,3. Levels 1,2,3 are the same notation as Level
0, except they are more specific and give more details about the system.
| Review Questions On Data Flow Diagrams Question #1 Data Flow Diagrams dipict the information flow of data through what states? Answer Data Flow Diagrams dipict the flow data throughout a software system, from the inputs of the system, to the outputs. Question #2 How is a process represented in a Data Flow Diagram? Answer A process is represented by a circle in basic Data Flow notation. Refer to the chart above. Question #3 Level 0 of a Data flow Diagram should show what? Answer Level 0 of a Data Flow Diagram should show the basic inputs and outputs of the general software sytem. |