Diversity and dependability
designing fault tolerance in any system or process has two
aspects:
• structure (redundancy) :
ensuring that given a potential error there is someone/
something in charge of detecting[, stopping[, correcting ]] it
• diversity:
containing the risk of the protective elements failing
together with the ones to be protected
Lorenzo Strigini
Printed 06/28/01, 03:06 PM
slide 1
Diversity and dependability - 2
two aspects in studying diversity:
• the goal:
high dependability of the fault-tolerant system/process,
through low correlation – diversity – between failures of
redundant parts.
Problem: how do we assess it?
• the means:
diversity in how components (including humans) and tasks
are made [or operated].
Problem: how effective [a certain form of] “means diversity”
is towards the goal?
Lorenzo Strigini
Printed 06/28/01, 03:06 PM
slide 2
Diversity RT
Sites: City (co-ordinator), Newcastle, Edinburgh, Lancaster
Background: Basis of formal probabilistic modelling mostly
developed at City
Interdisciplinary contribution: reliability, computing,
psychology, sociology
Application: human-computer systems, system development
and V&V, arguments
Interactions with non-DIRC teams (UCL, U. Valladolid, ...)
and projects : DOTS, DISPO, ..
Lorenzo Strigini
Printed 06/28/01, 03:06 PM
slide 3
Applications
• human-computer diversity (with advisory tools)
• computer-computer diversity and diversity within
development process
– evaluation, development guidance, effect of diversity among users,
effectiveness with off-the-shelf components, effect of diverse goalsetting
• diversity in arguments
Lorenzo Strigini
Printed 06/28/01, 03:06 PM
slide 4
Outputs
• conference, journal publications - multiple audiences
• [ related parts in Structure theme book ]
• to match planned Diversity outputs
– book-size output on the mathematical modelling
– long discussion paper on the broader interdisciplinary aspects
+ could evolve into a DIRC book or a xxxx pack/box ... the same thing as
the responsibility theme plans
Lorenzo Strigini
Printed 06/28/01, 03:06 PM
slide 5
Programme
• 9.35 Diversity Intro Lorenzo Strigini
• 9.50 M.J.P. van der Meulen et al: The Effectiveness of
Choice of Language as a Diversity Seeking Decision
• 10.15 A. Povyakalo, E. Alberdi, L. Strigini: Some difficult
decisions are easier without computer support
• 10.40 David Greathead, Budi Arief and Joey Coleman
TA Weinberg
• 11.05 Coffee
• 11.35 E. Alberdi, R.Bloomfield, M. van der Meulen, B.
Littlewood: A study of confidence in safety judgements
• 12.00 Richard Paul:
Self Organisation in Large Scale Peer-to-Peer Systems
• 12.25 P. Bagnall, G. Dewsbury and I. Sommerville:
The Limits of Personas
Lorenzo Strigini
Printed 06/28/01, 03:06 PM
slide 6