Littlewood, B., Popov, P., and Strigini, L. (2001). Modelling software design diversity: a review. ACM Computing Surveys, 33(2):177--208. Home/Search Document Details and Download
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A Discussion of Practices for Enhancing Diversity in.. - Littlewood, Strigini (2000) Self-citation (Littlewood Strigini) (Correct)
....separation between version developments, to protect them from any common influence (apart from the high level requirements that they need to share) Actually, supporters of independent development of versions often support forced diversity DSDs. Mathematical models [Littlewood Miller 1989, Littlewood et al. 2001] confirm that forced diversity is better (in a specific, precise sense) than simple separation. Even with fully (statistically) independent developments, we should expect positive correlation between version failures. But forced diversity is, mathematically speaking, a way of introducing a ....
....correlation) between failures. So, the phrase independent development often leads to confusion in these arguments and should be used with care. 1.4 Conceptual models of diversity We briefly recall here the basic models that inform the discussion in this paper. An extensive explanation is in [Littlewood et al. 2001]. A common concept is that of possible demands forming a demand space. Each point (demand) in this many dimensional space can be thought of as completely characterising a particular physical demand. For instance, for a reactor protection system a demand would be a vector of temperatures, ....
B. Littlewood, P. Popov and L. Strigini, "Modelling software design diversity - a review", ACM Computing Surveys, to appear, 2001.
Assessing the Reliability of Diverse Fault-Tolerant Systems - Bev Littlewood Peter (2000) (1 citation) Self-citation (Littlewood Popov Strigini) (Correct)
....application and clarifies some non intuitive issues about reliability assessment for fault tolerant software. 1. Introduction Design diversity between the redundant channels of a fault tolerant architecture appears to be an effective way of improving the dependability of software based systems [Littlewood et al. 2000b] However, it does not simplify the problem of assessing the reliability or safety of a specific system, e.g. for the purposes of licensing. Consider for instance a two channel, 1 out of 2, software based diverse system, as could be for instance a protection system (Fig. 1) we will use this ....
....and multiply them together. Evidence of even modest reliability of the channels would suffice to claim much higher reliability for the system. But assuming independent failures has been shown to be completely unrealistic by both experiments [Knight Leveson 1986] and theoretical modelling [Littlewood et al. 2000b] Positive correlation between channel failures should normally be expected, essentially because, for the builders of diverse versions of a program, some demands will be more difficult more error prone than others. So, even if diverse versions (channel software designs) are produced ....
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B. Littlewood, P. Popov and L. Strigini, "Modelling software design diversity - a review", ACM Computing Surveys, (to appear) 2000.
Design Diversity: an Update from Research on Reliability.. - Bev Littlewood Peter (2001) (2 citations) Self-citation (Littlewood Popov Strigini) (Correct)
....reliability of diverse systems to gain insight for supporting decisions. This paper is meant as a short summary of these results to date; mathematical details are available in several published papers. For a summary of previous results and references to previous literature, we refer the reader to [Littlewood 2001; Littlewood 1996] There are two kinds of open technical questions of practical interest: achievement of reliability: a manager or designer wishing to apply diversity has no well founded guidance as to which methods will be most effective or cost effective, among the many that are available. ....
....it This would be attractive in applications where very high reliability is required; alternatively, does it deliver a reliability improvement more cost effectively than alternative techniques 2 . 1 Independent Faults Models The EL and LM reliability models provide useful insight (see [Littlewood 2001], but have at least two limitations: They predict the average [un]reliability of versions and pairs of versions. To quantify the risk of exceeding a desired upper bound on failure probability, we need instead distributions of the pfd. They use parameters that would be unknown in practice ....
Littlewood B., Popov P., Strigini L.: Modelling software design diversity - a review. ACM Computing Surveys: to appear, 2001.
Observational Models of Requirements Evolution - Felici (2004) (Correct)
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Littlewood, B., Popov, P., and Strigini, L. (2001). Modelling software design diversity: a review. ACM Computing Surveys, 33(2):177--208.
A Formal Framework for Requirements Evolution - Felici (2003) (Correct)
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Bev Littlewood, Peter Popov, and Lorenzo Strigini. Modelling software design diversity: a review. ACM Computing Surveys, 33(2):177--208, 2001.
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