Introduction to Critical Systems Engineering (CS 5032 2012)
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This document provides an overview of a course on critical systems engineering. The course aims to help students understand critical systems, dependability, and security engineering principles. It will cover topics like requirements, human error, dependability assurance methods, and organizational failures. The course involves weekly 3-hour sessions and assessments include an exam and two coursework assignments.
Introduction to Critical Systems Engineering (CS 5032 2012)
- 1. Critical Systems Engineering Prof Ian Sommerville Dr John Rooksby Critical systems engineering, 2012 Slide 1
- 2. Course aims • When you have completed this course, you should: – understand what is meant by a critical system and have learned about different types of critical systems. – understand the fundamental concepts of system dependability and security and know about the key technical activities – specification, development and assurance - in critical systems engineering. – understand that critical systems are usually not simply technical systems but are socio-technical systems that include people and processes and are profoundly affected by organisational politics and policies. Critical systems engineering, 2012 Slide 2
- 3. Presentation • 3 hour slot, one afternoon per week (normally Thursdays) from 13.30 to 16.30. Short breaks at 14.25 and 15.35. • Benefits of this approach – Gives time for coverage of a topic so that you don’t forget material between lectures – Provides an opportunity to integrate work on case studies with the lecture material – Allows time for class exercises where required • Problems – More tiring for students (and lecturer) than separate lecture slots Critical systems engineering, 2012 Slide 3
- 4. Course topics • Introduction to critical systems (IS), System failure (JR) • Requirements engineering, dependability concepts (IS) • Human error and reliability (JR) • Dependability specification (IS) • Learning from failure (JR) • Dependability engineering, fault tolerant system architectures (IS) Critical systems engineering, 2012 Slide 4
- 5. Course topics • Organisations and organisational failure (JR) • Security engineering (IS) • Methods of dependability assurance, dependability cases (IS) • Critical infrastructure and the internet (JR) Critical systems engineering, 2012 Slide 5
- 6. Assessment • Examination (40%) – Covering all topics in the course • Coursework (60%) – Two pieces of coursework – 1 on the technical and 1 on the socio-technical aspect of the course. Each will be of equal weight (30%) Critical systems engineering, 2012 Slide 6
- 7. Web site http://www.cs.st- andrews.ac.uk/~ifs/Teaching/MScCritSysEng2012/index. html Copies of slides are on Slideshare (as well as studres) and will be linked from the course web site. Twitter: @StACS5032CritSy Critical systems engineering, 2012 Slide 7
- 8. Critical systems Critical systems engineering, 2012 Slide 8
- 9. Critical system essentials Safety The system should not harm people or the system’s environment Reliability Availability The system must operate without The system must be available to serious failures deliver services when requested to do so Security The system must be able to protect itself and its data from malicious use Critical systems engineering, 2012 Slide 9
- 10. Classes of critical system • Safety-critical systems – Failure results in loss of life, injury or damage to the environment e.g. chemical plant protection system; • Mission-critical systems – Failure results in failure of some goal-directed activity e.g. spacecraft navigation system; • Business-critical systems – Failure results in high economic losses e.g. customer accounting system in a bank; • Infrastructure systems – Failure results in a loss of infrastructure capability e.g. power distribution control system, broadband communications, etc. Critical systems engineering, 2012 Slide 10
- 11. Critical systems stack Critical system External systems X Operating system and middleware System hardware Infrastructure systems Physical infrastructure Critical systems engineering, 2012 Slide 11
- 12. System dependencies • Independent critical systems – Infrastructure/hardware is part of the system – System operation is not dependent on external systems – Embedded control systems such as those in medical devices • Critical software systems – Usually rely on commodity hardware/OS – System operation is dependent on external infrastructure provision – Hospital appointments system Critical systems engineering, 2012 Slide 12
- 13. Systems of systems • A critical system is rarely a single system but is a network of several software-intensive systems as well as infrastructure systems • Systems that support organisational needs (e.g. an inter-bank payments system) have to be designed to be robust so that they can cope with failures and unavailability in the other systems on which they depend Critical systems engineering, 2012 Slide 13
- 14. Systems of systems • Systems of systems (SoS) are complex socio- technical systems with – Different owners and management policies – Distributed operation – Heterogeneous hardware and software • Individual systems may be part of several SoS so – Conflicting requirements from different uses of the system – Complex negotations may be required when system changes are to be made Critical systems engineering, 2012 Slide 14
- 15. Socio-technical systems • Socio-technical systems include IT systems and the social and organisational environment in which these systems are used • Key influences are human behaviour, organisational processes and policies, regulations, cultur e Critical systems engineering, 2012 Slide 15
- 16. Socio-technical systems Social and political environment Laws, regulations, custom & practice System Business users Software-intensive system processes Organisational policies and culture Organisational strategies and goals Critical systems engineering, 2012 Slide 16
- 17. Regulation • Regulators are government-appointed bodies whose job is to ensure that companies and other bodies conform to national and international laws. • This normally involves interpreting the law and government policy and establishing standards and regulations that must be followed by industry. • Examples of regulators – Data protection authority – Civil Aviation authority – Bank of England / Financial Services Authority – Ofgen – electricity and gas regulator Critical systems engineering, 2012 Slide 17
- 18. Regulators and critical systems • Some critical systems may have to be certified by regulators before they are put into use. This is particularly true for safety-critical systems. • This means that the regulators check that the system is conformant to current regulations and standards. – This normally involves the system developers producing evidence (a safety case or a dependability case e.g.) that demonstrates that the system is dependable. • Examples of certifiers – Civil Aviation Authority – aircraft systems – Medical Devices Directorate – medical devices and instruments Critical systems engineering, 2012 Slide 18
- 19. System criticality • Primary critical systems – Systems where system failure leads directly to an incident that has an associated loss of some kind – Typically, these are control systems or systems that are closely associated with a control system – Example – failure of engine management system in a car causes engine to cut out while driving • Secondary critical systems – Systems whose failure may (but need not) lead to failure in an associated system that then leads to loss of some kind – Example – medical information system that maintains incorrect information about treatment Critical systems engineering, 2012 Slide 19
- 20. Critical systems engineering • Focus is on the use of techniques and methods to develop dependable and secure systems. • The costs of critical system failure are so high that development methods may be used that are not cost- effective for other types of system. • An important aim for many critical systems is certification and the development process has to be geared to achieving such certification. • Certification costs can exceed development costs. Critical systems engineering, 2012 Slide 20
- 21. Software engineering for critical systems • Formal methods for systems specification and analysis. • Use of specialized tools such as model checkers and static analyzers. • Risk-driven approach to system specification and management. • Argumentation systems to support the development of dependability cases. • Disciplined configuration management of all software and hardware. • Detailed process record keeping. Critical systems engineering, 2012 Slide 21
- 22. Denver airport baggage system • System to control baggage transfer at the (then new) Denver airport in the USA. • Example system illustrating some of the issues and problems that arise with complex socio-technical critical systems. • This is a business critical system – the effective functioning of the airport relies on its baggage handling system. Critical systems engineering, 2012 Slide 22
- 23. System overview • New baggage handling system, which was software controlled, based on individual baggage carts rather than conveyor belts. • Intention was automated handling so that there was no manual handling of bags from plane to passenger. • Very complex hardware/software system procured from several different companies. • Encountered complex organisational, hardware and software problems. Critical systems engineering, 2012 Slide 23
- 24. “Denver airport saw the future: It didn’t work” – Baggage system did not recognise blockages and simply continued to unload bags – Bags fell off the carts due to timing problems – System loaded bags onto carts that were already full • At the time of the airport opening, only a very limited version of the system was available. – This system had a 10% error rate (i.e. 10% of bags were delivered to the wrong place) • Airport 18 months late opening • System abandoned in 2005 Critical systems engineering, 2012 Slide 24
- 25. Key points • Economic and human activities are increasingly dependent on software-intensive systems. These can be thought of as critical systems. • For critical systems, the costs of failure are likely to significantly exceed the costs of system development and operation. • Consequently, the dependability and security of the system are the most important development considerations. • Critical systems are often subject to external regulation. Critical systems engineering, 2012 Slide 25
Editor's Notes
- #9: The effective functioning of our personal lives, society and economy is now dependent on software-intensive systemsMany of these systems are critical systems – systems where failure or lack of availability has a serious human, environmental or economic effect.Examples of critical systemsControl systems for complex equipment, such as an aircraft flight control systemInfrastructure systems that manage national infrastructure (power, water, telecommunications, railways, etc.)Healthcare systems that manage patient informationAlso give examples of non-critical systems e.g. games, PC applications,