1. Newton's Law of Motion in Software Development Processes?
CS 690S Computer Science Seminar
Aditya P. Mathur (CS)
in collaboration with …
João Cangussu (CS)
Ray. A. DeCarlo (ECE)
Monday November 5, 2001
Software Process Control

2. Software Process Control
Research Question
Can we control the Software Development Process in a manner similar to how physical systems and processes are controlled ?
The fundamental control problem (Ref: Control System Design by G. C. Goodwin et al., Prentice Hall, 2001)
The central problem in control is to find a technically feasible way to act on a given process so that the process adheres, as closely as possible to some desired behavior. Furthermore, this approximate behavior should be achieved in the face of uncertainty of the process and in the presence of uncontrollable external disturbances acting on the process.
Software Process Control

3. Research Methodology [1]
Understand how physical systems are controlled?
2. Understand how software systems relate to physical systems. Are there similarities? Are there differences?
3. Understand the theory and practice of the control of physical systems.
4. Can we borrow from this theory? If “yes,” then proceed further, else drink coffee or tea and think of another research direction.
5. Adapt control theory to the control of SDP and develop models and methods to control the SDP.
6. Study the behavior of the models and methods in real-life settings.
Software Process Control

4. Research Methodology [2]
Improve the model and methods.
Repeat steps 6 and 7 until you are thoroughly bored or get rich.
Software Process Control

5. Software Process Control
Feedback Control -
Required
Quality
Specifications
Observed
Quality
Effort +
Program
f(e)
Additional
effort
What is f ?
Software Process Control

6. Software Development Process: Definitions
A Software Development Process (SDP) is a sequence of well defined activities used in the production of software.
An SDP usually consists of several sub-processes that may or may not operate in a sequence. The Design Process, the Software Test Process, and the Configuration Management Process are examples of sub-processes of the SDP.
Software Process Control

7. Software Development Process: A Life Cycle
Requirements
Elicitation
Requirements
Analysis
Design
Code/Unit test
Integrate/Test
System test
More test
Deploy
Not all feedback loops
are shown.
Software Process Control

8. Software Process Control
Current Focus
Software Test Process (STP): System test phase
Objective:
Control the STP so that the quality of the tested software is as desired.
Quantification of quality of software:
Number of remaining errors
Reliability
Software Process Control

9. Software Process Control
Problem Scenario
remaining errors
r - number of
t- time t0 r0
observed
approximation
schedule set by
the manager rf
cp1
cp2
cp3
cp4
cp5
cp6
cp7
cp8
cp9
deadline
cpi = check point i
Software Process Control

10. Software Process Control
Our Approach
Actual STP
Controller
rerror(t)
’
w’f +
wf+wf
+
STP State Model
robserved(t)
rexpected(t) sc r0
Initial
Settings
(wf,) 
wf
Test Manager
Software Process Control

11. Physical and Software Systems: An Analogy
Dashpot
External force
To err is
Human.
Block
Rigid surface
Spring
Software
Xequilibrium
Spring Force
Effective Test Effort
Xcurrent
X: Position
Number of remaining
errors
Mass of the block
Software complexity
Quality of the
test process
Viscosity
Software Process Control

12. Physical Systems: Control
Controllability
Is it possible to control X (r) by adjusting Y (workforce and process quality)?
Observability
Does the system have distinct states that cannot be unambiguously identified by the controller ?
Robustness
Will control be regained satisfactorily after an unexpected disturbance?
Software Process Control

13. Physical Systems: Laws of Motion [1]
First Law:
Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
Does not apply to testing because the number of errors does not change when no external effort is applied to the application.
Software Process Control

14. Physical Systems: Laws of Motion [2]
Newton’s Second Law:
The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma.
CDM’s First Law:
The relationship between an complexity Sc of an applications, its rate of reduction in the number of remaining errors, and the applied effort E is E=Sc . r ..
Software Process Control

15. Physical Systems: Laws of Motion [3]
Third Law:
For every action force, there is an equal and
opposite reaction force.
When an effort is applied to test software, it leads to fatigue on the tester.
This is not a scientific relationship.
Software Process Control

16. Assumption I: CDM’s First Law
The magnitude of the rate of decrease of the remaining errors
is directly proportional to the net applied effort and inversely
proportional to the complexity of the program under test.
This is derived from Newton’s Second Law of motion.
Software Process Control

17. Assumption II: CDM’s Second Law
Analogy with the spring:
The magnitude of the effective test effort is proportional to the
product of the applied work force and number of remaining
errors.
for an appropriate .
Software Process Control

18. Assumption III: CDM’s Third Law
Analogy with the dashpot:
The error reduction resistance is proportional to the error
reduction velocity and inversely proportional to the overall
quality of the test phase.
for an appropriate .
Software Process Control

19. Software Process Control
State Model
: Disturbance
Software Process Control

20. Computing the feedback
Software Process Control

21. Case Study II: Razorfish Project Description
Project Goal: translate 4 million lines
of Cobol code to SAP/R3
A tool has been developed to achieve
the goal of this project.
Goal of the test process: (a) Test the generated code, not
the tool. (b) Reduce the number of errors by about 85%.
Software Process Control

22. Validation: Razorfish Project Testing Process
continue
testing
yes =
output 1
output 2 no
run
run
modify
SCobol
Transformer
SSAP R/3
input
Select a Test Profile
Software Process Control

23. Case Study II: Razorfish Project Results
If the process parameters are not altered then the goal is reached in about 35 weeks.
85% reduction achieved.
Software Process Control

24. Alternatives from Feedback: STP Quality
Improving quality alone will not help in
achieving the goal.
Desired eigenvalue=-0.152
Software Process Control

25. Alternatives from Feedback: Workforce
Desired eigenvalue=-0.152
Changing the workforce alone can produce the desired results.
Software Process Control

26. Alternatives from Feedback: STP quality and workforce
Set of valid choices for changing the quality and the workforce
Software Process Control

27. Software Process Control
Summary
Analogy between physical and software systems presented.
The notion of feedback control of software processes introduced.
One case study described.
Parameter estimation techniques used for model calibration. Made use of system identification techniques.
Software Process Control

28. Software Process Control
Ongoing Research
Sensitivity analysis:
r is more sensitive to changes in the model parameters during the early stages of the test process than during the later stages.
An improvement in the quality of the STP is more effective than an increase in the workforce.
Brook’s Law was also observed during the analysis.
Expansion of the model to include the entire SDP.
Additional case studies.
Software Process Control