System success and failure

Success and failure
Ian Sommerville

Success and failure in sociotechnical systems, 2013

Slide 1

Non-determinism
•

A deterministic system is one where a given
sequence of inputs will always produce the same
sequence of outputs.

•

Software systems are deterministic;

•

Systems that include humans are non-deterministic


Slide 2

• A socio-technical system will not always
produce the same sequence of outputs
from the same input sequence


Slide 3

• Human operational behaviour
– People do not always behave in the same
way
– Their actions are determined by a range of
internal and external factors


Slide 4

• System changes
– System behaviour is unpredictable because
of frequent changes to hardware, software
and data in seperately managed systems or
components


Slide 5

Subjective behaviour
• Whether or not a system has is effective
in ‘doing its job’ depends on the
observer of a system


Slide 6

• Complex socio-technical systems serve
different stakeholder groups, which may have
conflicting objectives
• Behaviour that is effective for one group, may
be ineffective for another


Slide 7

Success criteria
•

Complex systems are developed to address ‘wicked
problems’ – problems where there cannot be a
complete specification.

•

Different stakeholders see the problem in different
ways and each has a partial understanding of the
issues affecting the system.


Slide 8

• Success is a judgment and cannot be
objectively measured.
• Success is judged using the effectiveness of
the system when deployed rather than judged
against the original reasons for procurement.


Slide 9

Conflicting views of success
• A medical information system may be
designed to support multiple, conflicting
goals
– Improve quality of care.

– Provide better information and care costs
and so increase revenue.

Slide 10


Slide 11

•

Fundamental conflict
–

–

•

To satisfy reporting goal, doctors and nurses had to provide
additional information over and above that required for
clinical purposes.
They had less time to interact with patients, so quality of care
reduced. System was not a success.

However, managers had better reports
–

System was a success from a managerial perspective.


Slide 12

What is failure?
•

A failure is ‘a deviation from a specification’.

•

An oracle can examine a specification, observe a
system’s behaviour and detect failures.

•

Failure is an absolute - the system has either
failed or it hasn’t


Slide 13


Slide 14

A hospital system
•

A hospital information system is designed to maintain
information about available beds for incoming
patients and to provide information about the number
of beds to the admissions unit.

•

It is assumed that the hospital has a number of empty
beds and this changes over time. The variable B
reflects the number of empty beds known to the
system.


Slide 15

•

Sometimes the system reports that the number of
empty beds is the actual number available;
sometimes the system reports that fewer than the
actual number are available .

•

When the system reports that an incorrect number of
beds are available, is this a failure?


Slide 16

• The percentage of system users who
considered the system’s incorrect
reporting of the number of available
beds to be a failure was 0%.


Slide 17

Bed management system
•

Mostly, the number did not matter so long as it was
greater than 1. What mattered was whether or not
patients could be admitted to the hospital.

•

When the hospital was very busy (available beds =
0), then people understood that it was practically
impossible for the system to be accurate.


Slide 18

Failure is a judgement
• Specifications are a gross simplification of
reality for complex systems.
• Users don’t read and don’t care about
specifications


Slide 19

•

Whether or not system behaviour should be
considered to be a failure, depends on the observer’s
judgment

•

This judgment depends on:
–

The observer’s expectations

–

The observer’s knowledge and experience

–

The observer’s role

–

The observer’s context or situation

–

The observer’s authority


Slide 20

Failures are inevitable
• Technical reasons
– When systems are composed of opaque and
uncontrolled components, the behaviour of these
components cannot be completely understood
– Failures often can be considered to be failures in data
rather than failures in behaviour


Slide 21


Slide 22

• Socio-technical reasons
– Changing contexts of use mean that the
judgement on what constitutes a failure changes
as the effectiveness of the system in supporting
work changes

– Different stakeholders will interpret the same
behaviour in different ways because of different
interpretations of ‘the problem’

Slide 23

Conflict inevitability
• It is usually impossible to establish a set of
requirements where all stakeholder conflicts
are resolved
• Therefore, successful operation of a system
for one set of stakeholders will inevitably
mean ‘failure’ for another set of stakeholders


Slide 24

Normal failures
•

‘Failures’

are not just catastrophic
events but normal, everyday system
behaviour that disrupts normal work and
that mean that people have to spend
more time on a task than necessary


Slide 25

A system failure occurs when a direct or
indirect user of a system has to carry out
extra work, over and above that normally
required to carry out some task, in
response to some inappropriate or
unexpected system behaviour

Slide 26

Summary
•

Success and failure are not absolute but depend on
the judgment of the observer

•

It is impossible to reconcile all conflicts in a complex
STS – therefore some stakeholders may consider
system behaviour as ‘failure’

•

Failures are normal and inevitable in system
operation


Slide 27

System success and failure

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