2. Critical systems
•
Systems whose failure or unavailability can lead to
loss of life, injury, environmental damage or serious
economic consequences for businesses or countries
•
Almost all public and private sector activities in
developed countries now rely on critical, softwareintensive systems
•
Long-lifetime systems
Critical systems engineering, 2013
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4. Critical systems engineering
• The focus in critical systems
engineering is on the use of techniques
and methods to develop dependable
and secure systems
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5. •
The costs of critical system failure are so high that
development methods may be used that are not costeffective for other types of system.
•
A key difference between critical systems engineering
and other types of software engineering is often the
need to demonstrate compliance to laws and
regulations.
Critical systems engineering, 2013
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6. 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.
Critical systems engineering, 2013
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8. System certification
• The regulators check that the system is
conformant to current regulations and
standards and that due care and
attention has been paid to making the
system safe
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9. System certification
• Some critical systems have to be ‘certified’ by
an external regulator before they can be put
into use
– Aviation systems
– Nuclear systems
– Railway systems
– (Some) medical systems
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10. Certification costs
•
Certification is very expensive as it involves preparing
detailed documents for the regulator
•
There may be several thousand pages of
documentation that must be created and analysed
•
Certification costs can be comparable or even exceed
the system development costs
Critical systems engineering, 2013
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11. • System owners and developers jointly
produce evidence (a safety case or a
dependability case) that demonstrates
to the regulator that a system is safe
and dependable
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12. Compliance
• Even when system do not need certification
before use, their owners may need to
demonstrate compliance with existing laws
and regulations
• This may involve collecting information about
the design and operation of a system
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14. Critical systems engineering
• System failure costs are high
– Additional costs during system development are
justified if these reduce the likelihood of failure
– Tools and techniques to reduce the chances of
failure that are not cost-effective for other systems
may be used
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15. • Systems last a long time
– This requires the use of stable technologies
and the development of extensive system
documentation
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16. • Systems must demonstrate compliance
– Product and process record keeping
– Safety and dependability case development
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17. Critical systems engineering
processes
• Usually plan-driven processes where each
process stage is planned and carefully
documented
• Agile processes are not suitable for critical
systems engineering although some agile
practices such as test-first development may
be used
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18. • It is importantto have a complete description
of the system requirements and specification
so that they can be checked and analysed
before development begins
• Disciplined configuration management of all
software and hardware is essential
Critical systems engineering, 2013
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19. Dependable systems
• Fault avoidance
• Fault detection and removal
• Fault tolerance
• Failure recovery and restart
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20. Software engineering techniques
• Formal methods for systems specification and
analysis
• Fault detection tools such as model checkers
and static analyzers
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22. • Fault-tolerant architectures and software
redundancy
• Argumentation systems to support the
development of dependability cases
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24. Summary
• Focuses on the use of techniques and
methods to develop dependable and secure
systems
• The CSE process may have to develop
information to satisfy a regulator that a
system is safe and compliant with regulations
Critical systems engineering, 2013
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25. • A plan-based process is normally used
• Techniques that are not used for other types
of system may be cost-effective for critical
systems
Critical systems engineering, 2013
Slide 25
