1. Systems Analysis and Design
National Diploma in
Systems Analysis and Design
Data Flow Diagrams
18/11/2018
By Dominique Stainton

2. Data Flow Diagrams
In order to aid in the development of a system you can produce a visual representation of the system in the form of a Data Flow Diagram.
This enables you to view the way that data flows around the system. (very similar to the low level method of a Flow Diagram, I.e. the logical way the system works).
18/11/2018
By Dominique Stainton

3. Data Flow Diagrams
On completion of your Level 1 diagram you need to evaluate whether you can decompose your diagram into a Level 2 diagram.
This process of evaluation continues until you reach the final level, the EPD.
18/11/2018
By Dominique Stainton

4. From the scenario you produced a Level 1 DFD.
Data Flow Diagrams
You were provided a scenario for a Boat Building Company of which you created a DFD.
From the scenario you produced a Level 1 DFD.
18/11/2018
By Dominique Stainton

5. Boat Building Company Level 1 Data Flow Diagram
Solution No.2
Specification
Quote (copy 1)
Letter of intent
BQ1 (completed) +
Quote (2) + drawing +
Materials spec
BQ1 (4) + Drawing +
materials specs 1
Sales Office
Deal with customer 2
Design Office
Produce drawing and
materials specification 3
Materials Office
Price Materials 4
Production Office A
Customer
BQ1 (1)
BQ1 (2) + Drawing + materials specs
BQ1 (3) + Drawing + materials specs B
Order Processing
System
As a design this is fine, however, it is possible to decompose each of the identified processes into sub-processes.
18/11/2018
By Dominique Stainton

6. Data Flow Diagrams
The purpose of decomposing a process is to show the detailed logic, i.e. how it works! 1
Sales Office
Deal with
Customer
We will concentrate on the Deal with Customer process.
18/11/2018
By Dominique Stainton

7. Data Flow Diagrams Data Flow Diagrams
Process 1
What we need to do is have a look inside the Sales Office process “Deal with a Customer”
Inside Process 1
18/11/2018
By Dominique Stainton

8. Data Flow Diagrams Data Flow Diagrams
We can now see what sub-processes are present, i.e. the detailed logic.
Process 1.1
Process 1.3
Process 1.2
18/11/2018
By Dominique Stainton

9. Data Flow Diagrams Data Flow Diagrams
This procedure of decomposing can continue for as long as there are sub-processes in evidence.
Process 1.1
Process 1.1.1
Process 1.1.2
Process 1.1.3
Inside process 1.1
18/11/2018
By Dominique Stainton

10. Data Flow Diagrams Data Flow Diagrams
The initial description will produce a high level DFD, Level 0 (Context) or Level 1.
By describing the purpose of each process identified you will start to identify any other subsequent sub-process.
This is an iterative process that continues until all sub-processes have been identified.
18/11/2018
By Dominique Stainton

11. The process name is the name of the process that is being decomposed.
Data Flow Diagrams
Data Flow Diagrams
The general rule of drawing the decomposed DFD is to draw a frame around the identified sub-processes with the process id and the process name.
The process name is the name of the process that is being decomposed.
18/11/2018
By Dominique Stainton

12. The name of the sub-processes is the location of the parent process:
Data Flow Diagrams
Data Flow Diagrams
The name of the sub-processes is the location of the parent process: 1
Deal with Customer 1
Sales Office
Deal with customer
1.1
Sales Office
Make out BQ1
18/11/2018
By Dominique Stainton

13. Data Flow Diagrams Data Flow Diagrams
This makes it easier to check that the data flows entering and leaving the DFD are correct.
18/11/2018
By Dominique Stainton

14. Produce drawing and material specs
Data Flow Diagrams
Data Flow Diagrams
Example 1
Deal with Customer
Customer
Specification
1.1
Sales Office
Make out BQ1
BQ1 2
Design Office
Produce drawing and material specs
18/11/2018
By Dominique Stainton

15. This can be achieved by describing each of the processes further.
Data Flow Diagrams
Data Flow Diagrams
The initial description for the Marine Construction quotation system was quite high and we do not know exactly how the Materials office and Production Office produce their estimates.
This can be achieved by describing each of the processes further.
18/11/2018
By Dominique Stainton

16. Data Flow Diagrams Data Flow Diagrams Try this example
The Materials Office activity takes some care to ensure that accurate costs are produced. Each material specification is checked against the stock card index system. Where sufficient stock is available to fulfil this quotation then the most recent invoice is used for the quote. If there is insufficient stock then the materials catalogue is used.
The Production Office take similar care. The drawing and material specification are used to create a work schedule with each operation of the job identified in terms of equipment used, time taken and labour grade needed. The work schedule is prepared and clipped into a ring binder. Using this work schedule each operation is costed by reference to the labour rates file (a rate depends on the labour grade). In addition, a cost is added depending on the equipment used (by reference to the quarterly cost report) to give a total cost per operation.
18/11/2018
By Dominique Stainton

17. Data Flow Diagrams Data Flow Diagrams
If you refer to the handout you will be able to see an example of the DFD’s for each of the Materials and Production Office.
As the sub-processes on the hand outs are the final level what symbol is missing from these sub-processes?
18/11/2018
By Dominique Stainton

18. All the rules for the processes still apply:
Data Flow Diagrams
Data Flow Diagrams
All the rules for the processes still apply:
Every process must have an input
Every process must have an output
Every process must have an identifier
Every process must have a descriptor
18/11/2018
By Dominique Stainton

19. You can identify each level of the DFD by the process identifier.
Data Flow Diagrams
Data Flow Diagrams
You can identify each level of the DFD by the process identifier. 1
Level 1 Process
1.1
Level 2 Process
1.1.1
Level 3 Process
Process Identifier
18/11/2018
By Dominique Stainton

20. Data Flow Diagrams Data Flow Diagrams Conclusion
Once a DFD has been constructed you need to further describe each process to see if it can be decomposed.
This is an iterative process that continues for as long as a process can be decomposed.
18/11/2018
By Dominique Stainton