CRITICAL SYSTEMMOHSIN KHOJA
(B00727876)
What is Critical System?
• “Safety-critical systems are those systems whose failure could result in loss of life, significant property damage, or damage to the environment”[1]
There are many well known example in following application areas:
ü Medical Devices
ü Aircraft Flight Control
ü Weapons
ü Nuclear Systems
Life-critical system
https://thmatters.wordpress.com/life-critical-system-verification/
Traditional Systems
• Traditional areas are considered as the home of safety critical systems. They includes medical care, commercial aircraft, nuclear power, and weapons. [1]
• Failure in these areas can quickly lead to human life being put in danger, loss of equipment, and so on.[1]
• Computer controlled robotic devices replace surgeons traditional tools and involve in procedures such as [1]
ühip replacementü spinal surgeryüophthalmic surgery.
Example of Traditional SystemThe Boeing 777
• "The Most Technologically Advanced Airplane In The World." [1]
• Safety-critical computer systems have contributed to this aircraft.[1]
• Following are the features of the air craft:[1]
ü Six primary flat-panel displays
ü have Several other smaller displays in the cockpit.
ü have Several major computerized systems to aid the pilot which includes flight management and enhanced ground proximity warning.
ü three separate channels for redundancy are used for primary flight control system
ü Each channel is implemented with three separate lanes, each of which uses different processors and different compilers.
ü Extensive networking provides the necessary communication between the different subsystems.
Non-traditional Systems
• loss of an aircraft will probably kill people, However loss of a telephone system could not kill people. But a protracted loss of 911 service will certainly result in serious injury or death.[1]
• Emergency 911 service is an example of a critical infrastructure application.[1]• There are other applications which are computerized and it failure can lead to extensive loss of
service. In some cases disruption can be very serious. Examples:[1]ü transportation controlü banking and financial systemsü electricity generation and distributionü telecommunications
Failure of Critical SystemTherec-25
• Used in treatment for cancer [3]
• Eleven Therac-25s machines were installed. [3]• five in the US and six in Canada. [3] • between June 1985 and January 1987, six known accidents involved massive
overdoses by the Therac-25 [3]• deaths and serious injuries were caused[3]
• They have been described as the worst series of radiation accidents in the 35-year history of medical accelerators[3]
• The machine was recalled in 1987 for extensive design changes, including hardware and software errors. [3]
Accidents History
• On 3 June 1985 patient in Marietta Georgia received overdose[3]• On 26 July 1985 Hamilton Ontario received overdose because of micro
switch failure[3]• December 1985 patient in Yakima Washington receives overdose and died[3]
• 21 March 1986 Tyler Texas, patient receives overdose and died later[3]• 11 March 1986 – second T accident, patient died 1 month later[3]• 17 January 1987 Yakima Washington receives overdose second time. [3]
Reasons for failure
• Lack of Experience [3][4]• Overconfidence in software controls[3][4]• No user involvement in design or testing[3][4]• Testing was not sufficient[3][4]• Poor handling of error messages[3][4]• Hardware settings were not visible clearly[3][4]• Lack of constraints[3][4]• Poor documentation[3][4]
Therec-25
Therec-25 [3]
Korean Air Flight 801
• Korean Air flight 801, a Boeing 747-300, crashed into Nimitz Hill, Guam while attempting a non precision approach to runway 6L at A.B. Won Guam International Airport. [2]
• 254 persons on board, 237 of which were passengers, only 23 passengers and 3 flight attendants survived. [2]
• Reason:[2]üMinimum safe altitude warning system (MSAW) had been inhibited
Lessons Learned
• Accident does not only happens because of errors made by the flight crew, but also because of the manner in which the FAA made software changes to the MSAW system.[2]
• In a safety-critical system is a integral component that cannot be changed without suitable analysis of the impact of the change.[2]
Other Accidents
• Dulles International Airport, 1994[2]
• Houston Intercontinental Airport, 1998[2]
ADAPTIVE SYSTEMSEHRISH KHAWAJA
(B00727829)
Adaptive system
• “An adaptive system is a system in which there is interaction between the system and its environment so that both make transitions to changing states”.[5]
• adaptive system is dynamic.[5]• adaptive system can be part of another system. [5]• Example:ürobot
EXAMPLE
• Robots showingvisitors of a museum a sequence of different objects or helping people in elderly homes to walk around in the corridors[5]
• Learning systems [5]• classifying the gender of humans using photos of their faces[5]• Recognising speech from recorded [5]• Automatic driving cars [5]• Biological systems such as earthquakes or forest fires[5]
Intelligent Agents
• new concept in artificial intelligence [5]
• DEFINATION:
“computer system that is situated in some environment, and that is capable of autonomous action in this environment in order to meet its design objectives”[5]
Characteristics of Agent
• Autonomy[5]
• Reactivity[5]
• Pro-activeness[5]
• Social Ability[5]
Total System Perspective
• An adaptive system (e.g. an agent) interacts with an environment. [5]
• Multiple agents[5]
• Example:[5]
üforest fire control
üthe entities are trees, fire-men, bulldozers, air-planes, fire, smoke columns, the weather etc.
Example
• Restaurant (changes according to environment)[5]
üentities are kitchen, tables, chairs, cook, waiter, lights, etc. [5]
ülights will dim if some romantic couple is sitting below them.[5]
ütables and chairs which can move by themselves automatically when a large group of people enters the restaurant[5]
An example: a room heater with a thermostat
• Thermostat for a room heater which regulates the temperature of a room. [5]
THE ADAPTIVE LIGHT BRACELET
• Water Jewel (Fluid intake reminder)[6]• A continuously illuminated light spot reminds the user to drink
regularly [6]• This is presented by a gradient from red (user drank two or more
hours ago) to green (user just drank).[6]• This application is able to control the brightness of the Reminder
LED at three different levels[6]
Multi-agent Systems
• Multiple agents which may work together to solve a problem, or they may be competing to get the best out of the situation for themselves.[5]
• ADVANTAGES:[5]
ü Robustness
ü Speed.
ü Simplicity to extend or modify the system.
ü Information hiding
Complex Adaptive Systems
“Some systems consisting of multiple interacting entities are called complex adaptive systems”[5]
DIFFERENCE BETWEEN COMPLEX ADAPTIVE SYSTEM AND MULTI AGENT SYSTEM
EXAMPLE (Mobile Tourist Guide)
• Mobile tourist guides allow users to identify points-of-interest (POIs) such as restaurants or accommodation most suited to their needs and constraints using a mobile device.[7]
• Adaptive user interfaces (AUIs), which monitor user behaviour in order to adapt the user interface[7]
• POInter [7]
VIDEO
REFERENCE1. Knight, J. C. (2002, May). Safety critical systems: challenges and directions. In Software Engineering,
2002. ICSE 2002. Proceedings of the 24rd International Conference on (pp. 547-550). IEEE.2. Greenwell, W. S. (2003). Learning lessons from accidents and incidents involving safety-critical software
systems (Doctoral dissertation, University of Virginia).3. Leveson, N. G., & Turner, C. S. (1993). An investigation of the Therac-25 accidents. Computer, 26(7), 18-
41.4. Weinberg, J. (n.d.). Retrieved from http://hci.cs.siue.edu/NSF/Files/Semester/Week13-2/PPT-
Text/Slide16.htmlWiering, M. A. (n.d.). Introduction to Adaptive Systems.5. Fortmann, J., Poppinga, B., Heuten, W., & Boll, S. (2015, July). Real-life experiences with an adaptive
light bracelet. In Proceedings of the 2015 British HCI Conference (pp. 138-146). ACM.6. Hill, R., & Wesson, J. (2010, October). A-POInter: an adaptive mobile tourist guide. In Proceedings of the
2010 Annual Research Conference of the South African Institute of Computer Scientists and Information Technologists (pp. 113-122). ACM.
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