SafetyCritical Software

1
Safety-Critical Software
Safety-Critical Software Status Report Patrick
R. H. Place Kyo C. Kang Software Engineering
Institute Software Engineering Volume 1 The
Development Process, 2nd Ed., pp. 257-269
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Requirements Engineering and Safety

• Development IAW Safety Standards Costs More
• System Engineering Goal Minimize safety-critical
  subsystems while maintaining required safety
  level for entire system
• Safety Issues must be considered from the start
• Safety concerns often conflict with performance
  and/or cost
• Hazards Risk Analysis must be performed
  independent of Performance and Cost Risk Analyses

3
Software Safety

• Safety is a System Issue
• Safety is Measured as Risk
• Reliability is Not Safety
• Software Need Not Be Perfect
• Safe Software Is Secure and Reliable
• Software Should Not Replace Hardware
• Development Software is Also Safety-Critical

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Hazard Analysis Techniques

• Hazard Identification
• The Delphi Technique
• Joint Application Design (JAD)
• Hazard and Operability Analysis

• Hazard Analysis
• Fault Tree Analysis
• Event Tree Analysis
• Failure Modes and Effects Analysis (FMEA)

5
Computer-Human Interface Software

• Computer-Human Interface Software
• Development Survey
• Robert J. Remington
• Lockheed Martin Missiles and Space
• Sunnyvale, California
• CHI Rapid Prototyping and Usability Laboratory
• Software Engineering Volume 1 The Development
  Process, 2nd Ed., pp. 271-283

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Importance of CHI

• Growing competitive pressure for improved user
  interfaces for computer software products in the
  marketplace
• Ease-of-use and ease-of-learning are key factors
• Graphical User Interface (GUI) implement these
  key factors, but can be difficult to build
• Delays in getting products to market cost
  companies in terms of lost revenues, lost
  credibility, and depressed stock value

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CHI Design

• Iterative Design Process
• Theories, Models, and Research Foundations
• CHI Guidelines, Standards and Style Guides
• Rapid Prototyping

8
CHI Implementation

• Development Tools
• Selection can be difficult and time-consuming
• Identify target GUI environment
• Decide on use of User Interface Management System
  (UIMS), Interactive Design Tools (IDT), or
  program with low-level tools, e.g. Xlib,MacApp,
  or MS Windows API
• Future Trends
• Deal mainly with graphical appearance and
  behavior
• Dont support construction of application classes
• Dont assist in proper use of Human Factors
  knowledge

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CHI Evaluation

• Usability Evaluation
• Systematic observation of a sample of the
  potential user population using the prototype
• Usability Tests are captured with video, audio,
  etc
• Users are encouraged to think aloud
• Can provide a clear identification of potentially
  serious usability problems and insight into
  possible solutions

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Software Design Standards

• IEEE Standard 1016-1998
• Recommended Practice for Software
• Design Descriptions
• H. Jack Barnard, Chair
• James A. Darling, Vice Chair
• Robert F. Metz, Secretary
• et al
• Sponsored by
• Software Engineering Standards Committee
• of the IEEE Computer Society
• Software Engineering Volume 1 The Development
  Process, 2nd Ed., pp. 285-293

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IEEE Recommended Practice for Software Design
Descriptions

• Scope
• References
• Definitions
• Considerations for Producing an SDD
• Design Description Information Content
• Design Description Organization

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Considerations for Producing an SDD

• Software Life Cycle
• SDD Within the Life Cycle
• Purpose of an SDD

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Design Description Information Content

• Entities
• Entities Attributes
• Identification
• Type
• Purpose
• Function
• Subordinates

• Dependencies
• Interface
• Resources
• Processing
• Data

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Design Description Organization

• Design Views
• Decomposition Description
• Dependency Description
• Interface Description
• Detailed Design Description