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Reliability and Safety Lessons Learned. Ways to Prevent Problems Good computer systems Good computer systems Good training Good training Accountability.

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Presentation on theme: "Reliability and Safety Lessons Learned. Ways to Prevent Problems Good computer systems Good computer systems Good training Good training Accountability."— Presentation transcript:

1 Reliability and Safety Lessons Learned

2 Ways to Prevent Problems Good computer systems Good computer systems Good training Good training Accountability Accountability Individual responsibility Individual responsibility Management responsibility Management responsibility IEEE Code of Ethics IEEE Code of Ethics

3 Increasing Reliability and Safety What goes wrong? What goes wrong? –Many lines of code and many programmers –See page 130 –Problems are managerial, technical, social, legal, ethical

4 OverconfidenceOverconfidence Unappreciative of risks Unappreciative of risks Ignore warnings Ignore warnings Don’t consult manuals Don’t consult manuals

5 Professional Techniques Use good software engineering techniques at all stages of development: Use good software engineering techniques at all stages of development: –specifications –design –implementation –documentation –testing

6 Professional Techniques Study the techniques and tools available Study the techniques and tools available Knowing or learning enough about the application field and the software or systems being used Knowing or learning enough about the application field and the software or systems being used

7 Why Study Failures? Provides technical lessons Provides technical lessons Leads to improved hardware and software products Leads to improved hardware and software products Provide ethical data Provide ethical data Lead to improved ethical codes/laws Lead to improved ethical codes/laws

8 Lessons Learned Accidents are not the result of unknown scientific principles but rather a failure to apply well-known engineering practices Accidents are not the result of unknown scientific principles but rather a failure to apply well-known engineering practices Accidents will not be prevented by technological fixes alone, requires control of all aspects of the development and operation of the system Accidents will not be prevented by technological fixes alone, requires control of all aspects of the development and operation of the system

9 Lessons Learned Software developers need to recognize the limitations of software, and use hardware safety mechanisms Software developers need to recognize the limitations of software, and use hardware safety mechanisms

10 User Interfaces and Human Factors Aircraft control systems Aircraft control systems –Pilot needs feedback to understand what the automated system is doing at any time –The system should behave as the pilot expects –Workload that is too low can be dangerous

11 Redundancy and Self- checking Redundancy - judging - expensive Redundancy - judging - expensive Complex systems collect information to diagnose and correct errors Complex systems collect information to diagnose and correct errors Audit trails are vital Audit trails are vital Detail records help protect against theft and help trace and correct errors Detail records help protect against theft and help trace and correct errors

12 Redundancy and Self- checking Designed to constantly monitor itself and correct problems automatically Designed to constantly monitor itself and correct problems automatically Half of the computing power is devoted to checking Half of the computing power is devoted to checking The rest for errors The rest for errors –closes off part of the system –reroutes –corrects problems and reroutes again

13 TestingTesting CRITICAL! CRITICAL! Principles and techniques exist Principles and techniques exist Can use another company to perform independent verification and validation Can use another company to perform independent verification and validation

14 Dangerous Tendencies Operators Operators –bypass check mechanisms through familiarity Technicians Technicians –Blame random mechanical or signal glitches rather than software Corporate Managers Corporate Managers –Initially deny and ignore - then cover up –Finally - deal with expensive fixes

15 Overall Lessons Learned Should not declare problem understood with first hypothesis Should not declare problem understood with first hypothesis Should not expect management to follow through on field reports Should not expect management to follow through on field reports Overconfidence in software leads to economical marginal designs Overconfidence in software leads to economical marginal designs

16 Overall Lessons Learned Enforcement of software engineering practices is often abysmal Enforcement of software engineering practices is often abysmal Basing risk assessments on individual subsystems often leads to unrealistic optimism Basing risk assessments on individual subsystems often leads to unrealistic optimism

17 Lessons for Systems Engineering Hardware backups valuable Hardware backups valuable Software must not be presumed innocent Software must not be presumed innocent Software errors related can be indistinguishable Software errors related can be indistinguishable Audit trails are critical Audit trails are critical Risk estimates are subjective Risk estimates are subjective User feedback is valuable User feedback is valuable

18 Lessons for Software Engineering Documentation should be on-going Documentation should be on-going Designs should be kept simple Designs should be kept simple Testing should be built into software Testing should be built into software Software must be tested out of system and in system Software must be tested out of system and in system Reuse of software should be tested like new software Reuse of software should be tested like new software

19 Lessons for Oversight Users are more likely to make initial observations than monitoring officials Users are more likely to make initial observations than monitoring officials Users need reliable information in order to be maximally valuable Users need reliable information in order to be maximally valuable


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