Quality Tactics

1
Quality Tactics

• SE 540 Software Architecture Mark Ardis,
  Rochester Institute of TechnologyFall 2007

2
Acknowledgements

• Some of the material in these slides is taken
  from Software Architecture in Practice, 2nd
  edition by Bass, Clements and Kazman.

3
Outline

• Availability
• Performance
• Security
• Modifiability
• Testability
• Usability

4
Availability

• Fault detection
• Fault recovery
• Fault prevention

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Fault Detection

• Ping/echo
• Heartbeat
• Exception

6
Fault Recovery - Preparation

• Voting
• Active redundancy (hot backup)
• Passive redundancy (warm backup)
• Spare

7
Fault Recovery - Reintroduction

• Shadow operation
• State resynchronization
• Checkpoint/rollback

8
Fault Prevention

• Removal from service
• Transactions
• Process monitor

9
Cartoon of the Day (1/2)
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Cartoon of the Day (2/2)
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Performance

• Resource demand
• Resource management
• Resource arbitration

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Resource Demand

• Increase computational efficiency
• Reduce computational overhead
• Manage event rate
• Control frequency of sampling
• Bound execution times
• Bound queue sizes

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Resource Management

• Introduce concurrency
• Maintain multiple copies of data or computations
• Increase available resources

14
Resource Arbitration

• Scheduling policy
• FIFO
• Fixed-priority
• semantic importance
• deadline monotonic
• rate monotonic
• Dynamic priority
• Static scheduling

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Security

• Resisting attacks
• Detecting attacks
• Recovering from an attack

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Resisting Attacks

• Authenticate users
• Authorize users
• Maintain data confidentiality
• Maintain integrity
• Limit exposure
• Limit access

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Detecting and Recovering

• Intrusion detection system - anomalous patterns
• Restoration - see availability tactics
• Identification - maintain audit trail

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Modifiability

• Localize changes
• Prevent ripple effects
• Defer binding time

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Localize Changes

• Maintain semantic coherence
• abstract common services
• Anticipate expected changes
• Generalize module
• Limit possible options

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Prevent Ripple Effects

• Hide information
• Maintain existing interfaces
• Restrict communication paths
• Use an intermediary

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Defer Binding Time

• Runtime registration
• Configuration files
• Polymorphism
• Component replacement
• Adherence to defined protocols

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Testability

• Manage Input/Output
• Record/playback
• Separate interface from implementation
• Specialize access
• Internal monitoring
• Built-in monitors

23
Usability

• Design time
• Separate UI from rest of system
• Runtime
• Support user initiative
• Cancel, Undo
• Support system initiative
• User/System/Task models