Impact of design decisions on software quality

1
Impact of design decisions on software quality
Wiebe Hordijk 12-10-2004
2
Goal of this talk

• Show you my research framework
• Show you the status of my PhD study
• Discuss research design ideas

3
Agenda

• Introduction
• Overall goal
• Theoretical framework
• Related work
• Research designs

4
Introduction
Job
PhD study
daysPerWeek 3 title ICT Consultant
mutualBenefit
daysPerWeek 2 startDate 1-1-2004 plannedEndDat
e 1-1-2008
CurrentAssignment
Project
client Ministry of Foreign Affairs interesting
true
5
Overall goal
To build software more predictably
To build better software
Why?
To investigate correlations between design
decisions and software quality
How?
Theoretical Framework
Empirical Research
Case study Research
Form
6
Example hypotheses

• Layered systems are more reusable than
  non-layered systems.
• Systems with a relational database are more
  reliable than systems with file storage.
• In the majority of systems above 500 function
  points, systems with a domain model have better
  changeability than systems with a transaction
  script.

7
Theoretical framework

• Why?
• Reusable Rationale Blocks
• Design Space outline
• Quality Attributes Indicators
• Examples

8
Theoretical framework Why
Refines
Enables
Research
Hyp. 1
Hyp. 2
Hyp. 3
Framework
Web Site
Help
Feedback
Projects
9
(No Transcript)
10
Quality Attributes
11
Quality Indicator example
12
Design Space outline example
13
Effects Table example Data Storage
14
Example Sorting Algorithm
15
Framework Class Diagram
16
Related work

• Patterns
• SEI Reasoning Frameworks
• Other design space theories
• QOC
• DRL
• IBIS

17
Research designs

• Criteria
• Difficulties
• Possible solutions
• Examples

18
Criteria for research designs

• Construct validity, internal validity, external
  validity, reliability
• Conclusion must corroborate, reject or refine
  hypothesis
• Research must be feasible
• Hypothesis must be
• Non-trivial
• Interesting to practitioners

19
Difficulties in this research

• Long chains of influence
• Many rival hypotheses
• Many variables
• Little data
• Finding data costs much effort

20
1 Reasoning Frameworks

• Described by SEI
• Deduct system properties from component
  properties
• Example Failure probability with n-version
  majority voting

21
Drawbacks of Reasoning Frameworks

• Only available for some attributes
• Do not start from design choices, but from
  component properties

22
2 Intermediate indicators

• designProblem
• Domain Logic Structure
• option Domain Model
• option Table Module
• option Transaction Script

intermediateIndicator Analysis Effort
intermediateIndicator Lines of Code changed
qualityIndicator Change Effort
Hypothesis
23
Intermediate Indicators for Reliability

• number of test cases/source lines of code (R1)
• number of test cases/number of requirements
• (R2)
• test lines of code/source lines of code (R3)
• number of asserts/source lines of code (R4).
• code coverage (C)
• Reliability 0.669 1.586R1 0.0513R2
  0.0290R3 0.192R4 0.0774C

N. Nagappan, 2004
24
3 Rationale Harvesting

• Lots of consultants and system designers document
  rationale
• This rationale can be generalized into rationale
  blocks
• The support for this rationale must be documented
• This will only yield weak support

25
Thank you!
Impact of design decisions on software quality
Wiebe Hordijk 12-10-2004