1. Data-Flow Oriented Design
“From DFD to Structure Chart”
TCS2411 Software Engineering

2. TCS2411 Software Engineering
Lecture Objectives
To describe the process of translating the DFDs to structure charts
To understand the systematic approach in producing the design from the analysis model
To understand the different types of conversion that can be done in producing the structure chart
TCS2411 Software Engineering

3. TCS2411 Software Engineering
Expanding the DFD
Initial analysis produces the Context Diagram and Level 1 DFD
In the design phase, the DFD is expanded to lower levels, giving more sub-processes within the original process
Level 1  Level 2  Level 3  …
Consistency is to be maintained from level to level
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4. TCS2411 Software Engineering
Example of Level 1 DFD
Member
application form
Process
Application
new member record
Members
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5. TCS2411 Software Engineering
Expanded to Level 2
Member
Members
formatted
new member
record
application
form
Get
Form
Check
Form
Assign
Code
Prepare
Record
Format
Record
application
details
checked
application
details
new
member
details
new
member
record
TCS2411 Software Engineering

6. TCS2411 Software Engineering
Five-Step Process
The type of information flow is established
Flow boundaries are indicated
The DFD is mapped into program structure
Control hierarchy is defined by factoring
Resultant structure is refined using design measures and heuristics
TCS2411 Software Engineering

7. Types of Information Flow
Transform Flow
Information enter at a point, transformed, and exit at another point
Path: incoming flow  central transform  outgoing flow
Transaction Flow
Single data item, transaction, triggers one of many paths
Path: incoming flow  transaction centre  action path
TCS2411 Software Engineering

8. TCS2411 Software Engineering
Transform Mapping
After transform flow is identified, identify the boundaries of incoming and outgoing flow
Incoming flow = Afferent flow
Outgoing flow = Efferent flow
In between the boundaries of the two is the central transform
TCS2411 Software Engineering

9. TCS2411 Software Engineering
Example of Boundaries
Member
Members
formatted
new member
record
application
form
Get
Form
Check
Form
Assign
Code
Prepare
Record
Format
Record
application
details
checked
application
details
new
member
details
new
member
record
Afferent flow
Central
transform
Efferent flow
TCS2411 Software Engineering

10. TCS2411 Software Engineering
First Level Factoring
Process
Membership
Application
Get
Application
Process
Application
Generate
New Member
TCS2411 Software Engineering

11. Second Level Factoring
Process
Membership
Application
Get
Application
Process
Application
Generate
New Member
Get
Application
Form
Check
Application
Generate
New
Record
Format
New
Record
TCS2411 Software Engineering

12. TCS2411 Software Engineering
Refinement
The hierarchy produced is then refined to improve the quality of the design
Modules could be exploded or imploded
Apply design concepts of module independence, good cohesion, minimal coupling, and ease of maintenance
TCS2411 Software Engineering

13. TCS2411 Software Engineering
Transaction Mapping
If transaction flow is identified, identify the transaction centre and flow characteristics of each action path
Similar to transform flow, boundaries are identified for incoming flow and the separate action paths
Each action path is a transform flow or transaction flow as well
TCS2411 Software Engineering

14. Example of Transaction Flow
action paths
user commands
read
user
command
invoke
command
processing
command
type
TCS2411 Software Engineering

15. TCS2411 Software Engineering
Transaction Mapping
transaction
control a
reception
path b b d
dispatcher d a c1 p p q q
TCS2411 Software Engineering

16. Factoring and Refining
Each action path has to be refined into a substructure, either by transform or transaction mapping
Similar to transaction flow, apply design concepts to improve quality of design
TCS2411 Software Engineering

17. Completing the Structure Chart
For each data flow on the DFD add exactly one data couple. Use the same data flow name
For each control module, decide how it will control subordinates
For modules that select one of several paths, show selection logic with a diamond attached to the link
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18. Design Postprocessing
A processing narrative must be developed for each module
Interface description is provided for each module
Define local and global data structures
All design restrictions/limitations noted
Conduct design review
Optimisation is considered
TCS2411 Software Engineering

19. TCS2411 Software Engineering
References
“Software Engineering: A Practitioner’s Approach” 5th Ed. by Roger S. Pressman, Mc-Graw-Hill, 2001
“Software Engineering” by Ian Sommerville, Addison-Wesley, 2001
“The Practical Guide to Structured Systems Design” by Meilir Page-Jones, Benjamin/Cummings, 1988
TCS2411 Software Engineering