A Formal Approach for Software Maintenance

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A Formal Approach for Software Maintenance

• Umer Waqar, Ferhat Khendek, Daniel Vincent
• Proceeding of the International Conference on
  Software Maintenance (ICSM 02)
• 2002. 7. 22
• Present by Sunae Lee

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Contents

• Introduction
• Background
• Overview of approach
• Three phases for approach
• Enriching SDL architectures
• Generating new SDL behavior from MSC
• Merging SDL behaviors
• Case Study Automatic Teller Machine
• Conclusion

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Introduction (1/2)

• Software systems evolve because user requirements
  change over time.
• New behavior has to preserve all the old behavior
  in the existing system.
• Extended transformational model.

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Introduction (2/2)

• A formal approach, can, not only be automated but
  also guarantees to enrich the system.
• This approach effectively shifts maintenance from
  code level to specification level.

SDL (design spec.)
Automated approach for maintenance
Enriched SDL spec.
MSC (capture new requirement)
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Background (1/4) SDL (Specification and
Description Language)

• Object-oriented formal language defined by ITU-T
  for specification of complex, real-time
  applications.
• SDL comprises four main hierarchical levels
• system, blocks, processes, procedures
• The Structural View of an SDL System.

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Background (2/4) SDL (Specification and
Description Language)

• A simple behavioral specification in SDL.

start
state
input
decision
transition
non-determinism
output
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Background (3/4) MSC (Message Sequence Chart)

• A simple specification in MSC.

condition
lifeline of a process instance
messages between process instances
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Background (4/4) Extension relation

• Conservative extension
• The new system can substitute the old one.
• Prohibition of new non-determinism in the new
  system specification.
• Process Extension Example

P4 is not an extension of P3.
P2 is an extension of P1.
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Overview of approach (1/2)

• Generating enriched SDL specifications.

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Overview of approach (2/2)

• Pre-phase - Enriching SDL architectures
• Second-phase Generating new SDL behavior from
  MSC
• Post-phase Merging SDL behaviors

Old SDL specification
Pre-phase
Enriched SDL structure
New MSC specification
New MSC specification
Second-phase (use MSC2SDL tool)
New SDL behavior
Enriched SDL structure
Old SDL behavior
Post-phase
Enriched SDL behavior
New SDL behavior
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Enriching SDL architectures (1/2)

• Developed algorithms and tool to enrich of SDL
  architecture.
• Done in an interactive manner with the designer.
• Old Architecture and New MSC

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Enriching SDL architectures (2/2)

• Enriched architecture

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Generating new SDL behavior from MSC

• The MSC2SDL tool is used to generate new SDL
  spec.
• From the new MSC and the enriched architecture.
• Example new behavior of Bank process generated
  by MSC2SDL

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Merging SDL behaviors (1/5)

• Rule 1 (similar transitions)
• Two similar transitions without any new behavior.

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Merging SDL behaviors (2/5)

• Rule 2 (same output signal sequence, different
  next state)
• The new transition differs from the old
  transition only by the next state.

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Merging SDL behaviors (3/5)

• Rule 3 (different output signal sequence, same
  next state)
• The new transition extends the output sequence of
  the corresponding old transition.

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Merging SDL behaviors (4/5)

• Rule 5 (different Input Signal)
• A new transition appended to the resulting
  specification.

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Merging SDL behaviors (5/5)

• Rule 9 (involving ANY)
• Same input signal as the old non-deterministic
  transition.
• Output signal sequence exists in the old
  transition but not going to the same state.

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Case study ATM (1/6)

• Old ATM architecture

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Case study ATM (2/6)

• Behavior of the old ATM and Bank process

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Case study ATM (3/6)

• Add deposit functionality to the existing ATM.
• MSC deposit

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Case study ATM (4/6)

• Pre-phase
• Enriched ATM architecture

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Case study ATM (5/6)

• MSC2SDL-phase
• New behaviors of ATM and Bank generated by MSC2SDL

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Case study ATM (6/6)

• Post-phase
• Enriched ATM and Bank processes

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Conclusion

• Introduced an approach for incremental design of
  SDL specifications from MSCs.
• Not complete. Can only apply some partial
  situation.
• Suggested 14 rules for merging SDL specifications
  based upon a formally defined extension relation.
• Doesnt give any verification about rules.
• Guarantees to preserve old behavior and prevents
  inclusion of new non-determinism in the enriched
  SDL
• However, a user may want another kind of
  enrichment.
• Future work may include development of an
  extended specialization.