Conceptual Models for the Reliability of Diverse Systems
- New Results
by Peter Popov and Lorenzo Strigini presented
at the 28-th annual Symposium on Fault-Tolerant Computing (FTCS'28), Munich,
Germany, June 1998. The full text of the paper is available for download in .pdf
format. The abstract is given below.
Abstract
We address problems in modelling the reliability of
multiple-version software, and present models intended to improve the
understanding of the various ways failure dependence between versions can arise.
The previous models, by Eckhardt and Lee and by Littlewood and Miller, described
what behaviour could be expected "on average" from a randomly chosen pair of
"independently generated" versions. Instead, we address the problem of
predicting the reliability of a specific pair of versions. The concept of
"variation of difficulty" between situations to which software may be subject is
central to the previous models cited. We show that it has even more far-reaching
implications than previously found. In particular, we consider the practical
implications of two phenomena: varying probabilities of failure over input
sub-domains or operating regimes; and positive correlation between successive
executions of control software. Our analysis provides some practical advice for
regulators, and useful insight into non-intuitive aspects of the failure process
of diverse software.
Estimating Bounds on the Reliability of Diverse
Systems
by Peter Popov, Lorenzo Strigini, John May and Silke
Kuball is a substantially enhanced version of the FTCS-98 paper, "Estimating
Bounds on the Reliability of Diverse Systems". It has been accepted for
publication in IEEE Transactions on Software Engineering. The full text in .pdf
is accessible provided the IEEE copyright retrictions are respected. The
abstract is given below.
Abstract
We address the problems of estimating the reliability of
multiple-version software, and improve the understanding of the various ways
failure dependence between versions can arise. Specifically, we step from the
previous conceptual models, which described what behaviour could be expected "on
average" from a randomly chosen pair of "independently generated" versions to
predictions using specific information about a given pair of versions. The
concept of "variation of difficulty" between situations to which software may be
subject is central to the previous models cited. We show that it has more
far-reaching implications than previously found.
We show the practical
implications of varying probabilities of failure over input subdomains or
operating regimes. A direct practical gain for designers, users and regulators
is the possibility of estimating upper and lower bounds on the reliability of a
two-versions system. In certain circumstances these will be narrower than could
be estimated with other methods.
Page maintained by: Peter Popov
Last modified 3 July 2002.