Cleanroom

1
Cleanroom

• SE 420, Formal Methods
• Mark Ardis, RIT

2
Harlan Mills
1919 - 1996
3
Mathematics and Programming

• Roman accounting
• "to go from programming as an instinctive,
  intuitive process to a more systematic,
  constructive process"

4
Cleanroom Method

• Incremental (spiral)
• Box structure specification and design
• Design verification
• No debugging
• Statistical testing

5
Design Verification

• Procedures in BDL are checked for correctness
  with their higher-level descriptions
• All boxes (and all procedures) describe functions
• Formal proofs of correctness can be performed
  (but often informal proofs are done, instead)

6
Verification of Sequence

• Given a high-level function f for statement
  do g h od
• Does g followed by h compute the same
  function as f?
• Example
• f(x) 2 x 7
• g(x) 2 x
• h(x) x 7

7
Verification of Selection

• Given a high-level function f for statement
• if ltcondgt thengelsehfi
• Whenever ltcondgt is true, does g compute the
  same function as f?
• Whenever ltcondgt is false, does h compute the
  same function as f?

8
Verification of Iteration

• Given a high-level function f for statement
• while ltcondgt dogod
• Whenever ltcondgt is true, does g followed by f
  compute the same function as f?
• Does the loop always terminate?
• Whenever ltcondgt is false, does the empty function
  compute the same function as f?

9
Industrial Use

• Used in a few areas of IBM
• Used by some military contractors
• Tried at NASA
• Continuing use on small safety-critical projects