Luigi Logrippo SITE

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Luigi LogrippoSITE

• Feature Interactions

luigi_at_site.uottawa.ca http//www.site.uottawa.ca/
luigi/
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Main idea

• Many software flaws can be discovered by making
  the logic precise and thoroughly examining it by
  the use of logic tools
• Formal methods
• Feature interactions are the result of logic
  flaws
• Inconsistency of specs
• Application areas
• Security
• New VoIP and Web based systems
• Many others

Do this
Do that
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Feature Interaction in Automotive

• Electronic Stability Program (ESP) and Cruise
  Control (CC)
• ESP Break if wheels slip on wet road
• CC Increase speed until cruise speed is reached
• FI detectable by the fact that the two features
  have contradicting requirements

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Protection rings in Bell-LaPadula security model
High security personnel uses delegation to
transfer access rights to lower security
personnel FI Delegation defeats BLP
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FI in communications
FI CF defeats OCS .
3. A gets connected to C
2. B forwards to C
1. A calls B
OCS Originating Call Screening CF Call Forward
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Infinite loops FIs

• Companies A, B and C have policies where each of
  them uses the next in a loop as suppliers of
  parts in excess of inventory
• This can start a chain reaction with potentially
  disastrous effects!

Send 800 pucks
Send 1000 hockey pucks
Send 400
Send 600 pucks
Send 400 pucks
FI subcontracting defeats itself
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Infinite loops FIs

• Companies A, B and C have policies where each of
  them uses the next in a loop as suppliers of
  parts in excess of inventory
• This can start a chain reaction with potentially
  disastrous effects!

Send 800 pucks
Send 1000 hockey pucks
Send 400
Send 600 pucks
Send 400 pucks
FI subcontracting defeats itself
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Presence communications features

• Alice call Bob urgently about meeting
  cancellation
• Bobs policy send to voice mail all calls that
  arrive when I am moving faster than 50Km/h
• FI Bobs policy defeats Alices urgent call
  policy
• (BTW our group has extensive experience on the
  design of presence features with complex policies)

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How to detect

• Specifications must be made precise!
• Sometimes they are already sufficiently precise,
  e.g. in a XML-based language
• E.g.BPEL
• Constraint Logic Programming
• Given a set of logic constraints, CPL tools can
  tell whether
• There is a solution, constraints are satisfiable
• There is no solution, in fact there is a
  counterexample

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How to solve

• Solution is a more complex problem, will depend
  from
• User intentions,
• Try to identify user goals
• May require an interactive system
• Solution methods will vary according to the
  application domain

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Conclusions

• Complex designs require the composition of
  complex features
• With a lot of user control on what will happen in
  different situation (user policies)
• Introduction of these features will require
  sophisticated methods to control different
  situations of feature conflicts