Critical systems video, 2013 Slide 1

Critical systems

Critical systems video, 2013 Slide 2

Critical system essentials

ReliabilityThe system must operate without serious failures

Availability The system must be available to deliver services when requested to do so

SafetyThe system should not harm people or the system’s environment

SecurityThe system must be able to protect itself and its data from malicious use

Critical systems video, 2013 Slide 3

Critical system essentials

Safety

The system should not harm people or the system’s environment

Critical systems video, 2013 Slide 4

Critical system essentials

Reliability

The system must operate without serious failures

Critical systems video, 2013 Slide 5

Critical system essentials

Availability

The system must be available to deliver services when requested to do so

Critical systems video, 2013 Slide 6

Critical system essentials

Security

The system must be able to protect itself and its data from malicious use

Critical systems video, 2013 Slide 7

Dependability

ReliabilityThe system must operate without serious failures

Availability The system must be available to deliver services when requested to do so

SafetyThe system should not harm people or the system’s environment

SecurityThe system must be able to protect itself and its data from malicious use

Critical systems video, 2013 Slide 8

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;

Critical systems video, 2013 Slide 9

Classes of critical 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.

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Critical systems stack

Physical infrastructure

Infrastructure systemsSystem hardware

Operating system and middleware

External systemsCritical system X

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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

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Critical software systems• Usually rely on commodity

hardware/OS• System operation is dependent

on external infrastructure provision

• Hospital appointments system

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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

Critical systems video, 2013 Slide 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

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Systems of systems• 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 video, 2013 Slide 16

Systems of 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 video, 2013 Slide 17

Summary• Critical systems are usually systems of

systems• Society depends on a range of critical

systems from control systems to infrastructure systems

• The more important characteristic of a critical system is its dependability, where dependability attributes are safety, reliability, availability and security

Critical systems video, 2013 Slide 18

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