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Presentation :. Analyzing Software Requirements Errors in Safety-Critical Embedded Systems. INTRODUCTION.

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  1. Presentation : Analyzing Software Requirements Errors in Safety-Critical Embedded Systems

  2. INTRODUCTION • A software error is defined to be a software related discrepancy between a computed, observed or a measured value or condition and the true specified, or theoretically correct value or condition • There are 3 types of errors: negligible, significant and catastrophically

  3. METHODOLOGY • Work of Nakajo and Kume on software error cause and effect relationship offers an appropriate framework for classifying software errors. • Their work analyses 3 points in the path from s/w error backwards to its source allowing classification of not only s/w errors but also human errors.

  4. OVERVIEW OF CLASSIFICATION • Program Faults • Human Error • Process Flaws

  5. PROGRAM FAULTS • Internal Faults :Syntax, Programming Language Semantics • Interface Faults:Interaction with other Software Components,Interaction with hardware in the system • Functional Faults:Operating Faults, Conditional Faults, Behavioral Faults

  6. Program Faults (Contd.) • Safety related errors account for 56% of total errors in Voyager and 48% in Galileo. • A few internal faults were also found during integration and system testing • The tables in the appendix of the paper provide a lot of statistical data is provided

  7. HUMAN ERROR • Coding Errors • Communication Errors • Within a Team • Between Teams • Requirements • Errors in Recognition • Errors in Deployment

  8. PROCESS FLAWS • Flaws in Inspection and Testing Methods • Inadequate Interface-Specification & Communication • Between Software Designers and Programmers • Between Software and Hardware Engineers • Requirements Not Identified or Understood • Incomplete Documentation • Missing Requirements • Inadequate Design

  9. RELATION BETWEEN PROGRAM FAULTS AND ROOT CAUSES: • Second step is to track backwards in time to find human factors involved in program faults • Interface faults human factors are mainly miscommunications between development/department teams.

  10. RELATION BETWEEN PROGRAM FAULTS AND ROOT CAUSES: (Contd.) • Safety related interface faults are largely due to communication errors between teams rather within teams (67% on voyager and 48% on Galileo) • Non-safety related errors are equally likely due to misunderstood hardware as well as software specifications.

  11. RELATION BETWEEN PROGRAM FAULTS AND ROOT CAUSES (Contd.) • Safety related functional faults are primarily due to errors in recognizing requirements. • Operational faults and behavioral faults are caused by errors in recognizing requirements more often than due to errors in development.-[Lutz 92]

  12. RELATION BETWEEN PROGRAM FAULTS AND ROOT CAUSES (Contd.) BOTTOM LINE: Difficulties with safety requirements are a root cause of safety-related software errors until integration and system testing is done.

  13. RELATION BETWEEN ROOT CAUSES AND PROCESS FLAWS: • The third step is to associate a pair of flaws to each program fault • This first element identifies the process flaw or inadequacy in control of the system complexity-[Lutz 92] • The second element identifies the associated process flaw in the comm. or development methods.-[Lutz 92]

  14. RELATION BETWEEN ROOT CAUSES AND PROCESS FLAWS: • Safety related interface faults which are the most common process flaws are not inadequately identified along with undocumented h/w behavior • Misunderstood requirements could lead to design flaws and may result in imprecise specifications

  15. COMPARISON OF RESULTS WITH PREVIOUS WORK • Role of interface specifications in controlling software was underestimated • Previous reports analyzed fairly simple systems in well-understood domains

  16. COMPARISON OF RESULTS WITH PREVIOUS WORK (Contd.) • Assumes that requirement specifications are correct • Distinction between causes of safety critical and non-safety critical s/w errors was not adequately investigated-[Lutz 92]

  17. Recommendations • Focus more on developing the interface between software and the system • Identify safety-critical hazards during requirement analysis

  18. Recommendations (Contd.) • Use formal specifications techniques in addition to natural-language software requirements • Promote informal communication among teams

  19. Recommendations (Contd.) • Teams must communicate better as requirements change • Include requirements for “defensive design”

  20. STRENGTH AND WEAKNESS • STREGNTHS • Detailed analysis of safety critical errors in spacecrafts and good classification of errors • WEAKNESS • Does not take into consideration the wide range of safety critical embedded systems

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