clean room software engineering

4. -Suhas Nayak

5. What is it?
Formal design and requirements methods
+
Statistical Usage Testing
______________________________
Little or No Defects

6. Why Cleanroom?
O Quality
O Most suitable for critical applications
O Increased Productivity
O Reduces Costs

7. Cleanroom Methodology
O Requirements Analysis
O High-level Design
O Detailed Design
O Coding by increment
O Pretest by increment
O Statistical Testing by increment

8. Incremental Development
Cycle
O Early and continual quality assessment
O Increased user feedback
O Repair any process related problems
O Allow requirements changes

9. Formal
specification
Develop s/w
increment
Establish
rerquirements
Deliver
software
Frozen
specification
Requirements change request

10. Cleanroom Principles - part 1
O Small teams
O independent specification, development, and
certification sub-teams
O Incremental development under statistical quality
control
O performance assessed during each increment
using measure like number of sequential error-
free test cases
O feedback is used for process improvement and
the development plan is adjusted as needed

11. Cleanroom Process Teams
O Specification team
O develops and maintains the system specification
O Development team
O develops and verifies software
O the software is not compiled or executes during
verification
O Certification team
O develops set of statistical test to exercise
software after development
O reliability growth models used to assess reliability

12. Cleanroom Principles - part 2
O Software development based on mathematical principles
O the box principle is used for specification and design
O formal verification is used to confirm correctness of
implementation of specification
O program correctness is verified by team reviews using
questionnaires
O Testing based on statistical principles
O operational usage profiles needed
O test cases are randomly generated from the usage
model
O failure data is interpreted using statistical models

13. Functional Specification
Modeling approach in cleanroom software
engineering uses a method called box
structure specification
OBlack Box
OState Box
OClear Box

14. Fig:
Box Structure Refinement
BB1
BB 1.1
BB1.2
BB1.n
BB.1.1.1
BB1.1.2
BB1.1.3
SB1.1.1
CB1.1.1.1
CB1.1.1.2
CB1.1.1.3

15. Cleanroom Strategy - part 1
O Increment planning.
O The project plan is built around the incremental
strategy.
O Requirements gathering.
O Customer requirements are elicited and refined
for each increment using traditional methods.
O Box structure specification.
O Box structures isolate and separate the definition
of behavior, data, and procedures at each level of
refinement.

16. Cleanroom Strategy - part 2
O Formal design.
O Specifications (black-boxes) are iteratively refined
to become architectural designs (state-boxes) and
component-level designs (clear boxes).
O Correctness verification.
O Correctness questions are asked and answered,
formal mathematical verification is used as
required.

17. Cleanroom Strategy - part 3
O Code generation, inspection, verification.
O Box structures are translated into program
language; inspections are used to ensure
conformance of code and boxes, as well as
syntactic correctness of code; followed by
correctness verification of the code.
O Statistical test planning.
O A suite of test cases is created to match the
probability distribution of the projected product
usage pattern.

18. Cleanroom Strategy - part 4
O Statistical use testing.
O A statistical sample of all possible test cases is
used rather than exhaustive testing.
O Certification.
O Once verification, inspection, and usage testing
are complete and all defects removed, the
increment is certified as ready for integration.

19. Cleanroom Process Overview
Construct
structured
program
Define
software
increments
Formally
verify
code
Integrate
increment
Formally
specify
system
Develop
operational
profile
Design
statistical
tests
Test
integrated
system
Error rework

20. Conclusion
O Key Characteristics of Cleanroom SE
O Incremental Development Life Cycle
O Defect Prevention: Quality Assessment thru
Statistical Testing
O Disciplined SE methods required to create
correct, verifiable software

21. Resources
O Software Engineering – Roger S Pressman
O www.suhas-angelus/blogspot.com

22. Question Time!!