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.