Functional decomposition

1
Functional decomposition

• (Pressman, Software Engineering,
• Chapter 14 - 14.7)
• Revised 8/15/2001

2
Structured analysis/design SA/SD

• Software design for a language where subroutines
  (procedures and functions) are the main
  structuring devices
• Intended to be as simple as possible
• Structured analysis is the analysis of the data
  flow between transforms
• Structured design is the construction of a
  subroutine hierarchy

3
Data-flow analysis

• A functional architecture typically consists of a
  hierarchy of subprograms represented as a
  structure chart.
• In a functional approach, architectural design
  then consists of translating a data flow diagram
  into a structure chart.
• Two types of data flow
• Transform flow
• Transaction flow

4
Transform flow

• This is the fundamental concept of data flow
  analysis
• An incoming flow of data passes through the
  afferent branch of transforms to a point of
  highest abstraction (transform center).
• From there, the outgoing dataflow passes through
  the efferent branch of transformations.

5
Transform flow
Transform center
Afferent branch
Efferent branch
6
Transaction flow

• For some types of data (typically in interactive
  systems) a choice of processing is based on
  transaction type. This choice occurs in a
  transaction center bubble.
• From there, one of a number of action paths is
  taken.

7
Transaction flow
Transaction center
Action paths
8
Structure chart

• The dataflow is converted into a hierarchical
  structure chart of subprograms calling each other

9
Afferent branch
Efferent branch
Central transform
10
Fragmentation problem

• The authors of structured analysis and design
  suggest that some modules in the structure chart
  be consolidated
• This often does not happen.
• The result is a multitude of small subroutines

11
Conclusion

• In some problems, the flow of data between
  computational elements - functions - is central.
• Functional decomposition then provides a way to
  structure the program into subprograms
• The dataflow approach (structured
  analysis/design) is often used for this
• To avoid fragmentation, small subprograms should
  be consolidated
• Each subprogram should be functionally cohesive.