Why do we need this course?

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Why we need this course?

COMP3530 - Systems Engineering for Software Engineers

Why do we need this course?

Shayne Flint

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1 Ian Sommerville, 1999

2 Denver Airport Baggage Handling System

3 London Ambulance Despatching System

4 Why is software a problem?

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Ian Sommerville

Systems engineering for software engineers

.

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Denver Airport Baggage Handling System

• Delayed opening of completed airport by 16 months • Added $560M USD to the cost of the airport

• The final system was no where near that originally planned

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This was a complex system

• over 17 miles of track, • 5.5 miles of conveyors, • 4000 baggage carts (telecarts), • 5000 electric motors,

• 2700 photocells,

• 59 bar code reader arrays, • 311 radio frequency readers, • more than 150 computers.

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Denver Airport Baggage Handling System

Other contributing factors

• In May 1992, the airlines and the city ordered a major revision of the

automated baggage system while it is under construction.

• 21 October 1992: a BAE superintendent complained that another

contractor was denying his crews access to the work site. Infighting continued through 1993.

• The baggage system continued to unload bags even though they were

jammed on the conveyor belt. This problem occurred because the photo eye at this location could not detect the pile of bags on the belt and hence could not signal the system to stop.

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Sommerville observes:

• ...we can see that the problems with this system were really much broader

than simply software problems.

• Blaming the delays and difficulties on poor software engineering

misrepresents reality.

• The system, as a whole, and not just the software failed to operate

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• The system could not cope with the load placed on it by normal use; • The response to emergency calls was several hours;

• Ambulance communications failed and ambulances were lost from the

system.

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London Ambulance Despatching System

This was also a complex system

• Largest ambulance service in the world

• Covers geographical area of over 600 square miles

• Resident population of 6.8 million people (greater during daytime,

especially central London);

• Carries over 5,000 patients every day;

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• the system relied on a technical communications infrastructure that was

overloaded and unable to cope easily with the demands that the CAD would place upon it particularly in a difficult communications environment such as London.

• Management clearly underestimated the difficulties involved in changing

the deeply ingrained culture of the London Ambulance Service and misjudged the industrial relations climate so that staff were alienated to the changes rather than brought on board.

• the early decision to achieve full CAD implementation in one phase was

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Why does software get the blame?

Sommerville observes:

• ... when we examine why the software is late, we see that the reasons are

often due to underlying systems engineering problems.

• In order to cope with other systems problems, demands are made for

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inevitable when the developers of the software must constantly accommodate change.

• New customer requirements emerge which have to be accommodated in

software because the hardware has already been designed and manufactured.

• The impact of the system on organisational processes may not have been

properly analysed.

• Hardware incompatibilities are discovered during system integration and

the software must be changed to ensure that the different hardware units can work together.

• Hardware fails to perform to its specification so additional processing by

the software is required.

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Why is software late and over-budget?

We must accept that other problems of systems engineering will inevitably mean that there will be demands for software changes at a late stage in the development process.

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As Sommerville says:

• Some students, especially those who are self-taught programmers, do not

appreciate the need for disciplined approaches to software development.

• They have a programming model which focuses solely on the software and they do not understand the relationships between software and other components of large, complex systems.

• Graduates from computer science and software engineering courses do not

understand the problems faced by engineers and managers from other disciplines.

• This means that communication is difficult and participation by software engineers in the systems engineering process is limited.

• Important decisions affecting system software may therefore be made without informed advice on the consequences for the software of these decisions.

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Systems Engineering for Software Engineers

Shayne Flint

Research School of Computer Science College of Engineering and Computer Science

The Australian National University Tel: +61-(0)2-6125-8183