System success and failure

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System success and failure

  1. 1. Success and failure Ian Sommerville Success and failure in sociotechnical systems, 2013 Slide 1
  2. 2. Non-determinism • A deterministic system is one where a given sequence of inputs will always produce the same sequence of outputs. • Software systems are deterministic; • Systems that include humans are non-deterministic Success and failure in sociotechnical systems, 2013 Slide 2
  3. 3. • A socio-technical system will not always produce the same sequence of outputs from the same input sequence Success and failure in sociotechnical systems, 2013 Slide 3
  4. 4. • Human operational behaviour – People do not always behave in the same way – Their actions are determined by a range of internal and external factors Success and failure in sociotechnical systems, 2013 Slide 4
  5. 5. • System changes – System behaviour is unpredictable because of frequent changes to hardware, software and data in seperately managed systems or components Success and failure in sociotechnical systems, 2013 Slide 5
  6. 6. Subjective behaviour • Whether or not a system has is effective in ‘doing its job’ depends on the observer of a system Success and failure in sociotechnical systems, 2013 Slide 6
  7. 7. • Complex socio-technical systems serve different stakeholder groups, which may have conflicting objectives • Behaviour that is effective for one group, may be ineffective for another Success and failure in sociotechnical systems, 2013 Slide 7
  8. 8. Success criteria • Complex systems are developed to address ‘wicked problems’ – problems where there cannot be a complete specification. • Different stakeholders see the problem in different ways and each has a partial understanding of the issues affecting the system. Success and failure in sociotechnical systems, 2013 Slide 8
  9. 9. • Success is a judgment and cannot be objectively measured. • Success is judged using the effectiveness of the system when deployed rather than judged against the original reasons for procurement. Success and failure in sociotechnical systems, 2013 Slide 9
  10. 10. Conflicting views of success • A medical information system may be designed to support multiple, conflicting goals – Improve quality of care. – Provide better information and care costs and so increase revenue. Success and failure in sociotechnical systems, 2013 Slide 10
  11. 11. Success and failure in sociotechnical systems, 2013 Slide 11
  12. 12. • Fundamental conflict – – • To satisfy reporting goal, doctors and nurses had to provide additional information over and above that required for clinical purposes. They had less time to interact with patients, so quality of care reduced. System was not a success. However, managers had better reports – System was a success from a managerial perspective. Success and failure in sociotechnical systems, 2013 Slide 12
  13. 13. What is failure? • A failure is ‘a deviation from a specification’. • An oracle can examine a specification, observe a system’s behaviour and detect failures. • Failure is an absolute - the system has either failed or it hasn’t Success and failure in sociotechnical systems, 2013 Slide 13
  14. 14. Success and failure in sociotechnical systems, 2013 Slide 14
  15. 15. A hospital system • A hospital information system is designed to maintain information about available beds for incoming patients and to provide information about the number of beds to the admissions unit. • It is assumed that the hospital has a number of empty beds and this changes over time. The variable B reflects the number of empty beds known to the system. Success and failure in sociotechnical systems, 2013 Slide 15
  16. 16. • Sometimes the system reports that the number of empty beds is the actual number available; sometimes the system reports that fewer than the actual number are available . • When the system reports that an incorrect number of beds are available, is this a failure? Success and failure in sociotechnical systems, 2013 Slide 16
  17. 17. • The percentage of system users who considered the system’s incorrect reporting of the number of available beds to be a failure was 0%. Success and failure in sociotechnical systems, 2013 Slide 17
  18. 18. Bed management system • Mostly, the number did not matter so long as it was greater than 1. What mattered was whether or not patients could be admitted to the hospital. • When the hospital was very busy (available beds = 0), then people understood that it was practically impossible for the system to be accurate. Success and failure in sociotechnical systems, 2013 Slide 18
  19. 19. Failure is a judgement • Specifications are a gross simplification of reality for complex systems. • Users don’t read and don’t care about specifications Success and failure in sociotechnical systems, 2013 Slide 19
  20. 20. • Whether or not system behaviour should be considered to be a failure, depends on the observer’s judgment • This judgment depends on: – The observer’s expectations – The observer’s knowledge and experience – The observer’s role – The observer’s context or situation – The observer’s authority Success and failure in sociotechnical systems, 2013 Slide 20
  21. 21. Failures are inevitable • Technical reasons – When systems are composed of opaque and uncontrolled components, the behaviour of these components cannot be completely understood – Failures often can be considered to be failures in data rather than failures in behaviour Success and failure in sociotechnical systems, 2013 Slide 21
  22. 22. Success and failure in sociotechnical systems, 2013 Slide 22
  23. 23. • Socio-technical reasons – Changing contexts of use mean that the judgement on what constitutes a failure changes as the effectiveness of the system in supporting work changes – Different stakeholders will interpret the same behaviour in different ways because of different interpretations of ‘the problem’ Success and failure in sociotechnical systems, 2013 Slide 23
  24. 24. Conflict inevitability • It is usually impossible to establish a set of requirements where all stakeholder conflicts are resolved • Therefore, successful operation of a system for one set of stakeholders will inevitably mean ‘failure’ for another set of stakeholders Success and failure in sociotechnical systems, 2013 Slide 24
  25. 25. Normal failures • ‘Failures’ are not just catastrophic events but normal, everyday system behaviour that disrupts normal work and that mean that people have to spend more time on a task than necessary Success and failure in sociotechnical systems, 2013 Slide 25
  26. 26. A system failure occurs when a direct or indirect user of a system has to carry out extra work, over and above that normally required to carry out some task, in response to some inappropriate or unexpected system behaviour Success and failure in sociotechnical systems, 2013 Slide 26
  27. 27. Summary • Success and failure are not absolute but depend on the judgment of the observer • It is impossible to reconcile all conflicts in a complex STS – therefore some stakeholders may consider system behaviour as ‘failure’ • Failures are normal and inevitable in system operation Success and failure in sociotechnical systems, 2013 Slide 27

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