Software dissimilarity

N-version programming is a system design technique that involves producing two or more software components that provide the same function, but in different ways. This approach is intended to avoid sources of common errors between redundant components. N-version programming is also referred to as multi-version software, dissimilar software, or software diversity. 

C2 P5 software dissimilarity compilers and link editors used for the generation of executable software are created by different publishers. 

In terms of safety and particularly integrity, the architecture of flight control computers is based on a eormnand chatmel and a monitoring charmel, with a requirement of dissimilarity between these two chaimels. Currently, this dissimilarity is demonstrated by the dissimilarity of the command channel software and of the monitoring chatmel software. Therefore, it seems possible, based on this software dissimilarity, to use identieal hardware resources of integrated modular avionics to meet the required safety level. 

Regarding dissimilar redundancy dissimilarity can be both in hardware and software. Software dissimilarity is achieved by producing two separate software lequirements/solutions and by the use of two separate teams. Increased workload is countered by being able to limit the amount of testing hy virtue of the replication of computation. The two software lines run asynchronously in two processes and their outputs are added or compared to ensure that no demand is made incorrectly. This achieves high integrity hut at the expense of avaUahUity, so that where passivity cannot be tolerated (e.g. fly-by-wire control systems) such architectures must have an alternative central lane in the event of a failure. 

Similarity is often used as a general term to encompass either similarity or dissimilarity or both (see Section 6.4.3, on similarity measures, below). The terms "proximity" and distance are used in statistical software packages, but have not gained wide acceptance in the chemical literature. Similarity and dissimilarity can in principle lead to different rankings. 

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The first application of a computational method to select structurally diverse compounds for purchase started in 1992 at the Upjohn Company, which predated the formation of Pharmacia Upjohn by about three years. The basic approach selected compounds using a method based upon maximum dissimilarity and was implemented using SAS software [11]. This later evolved into the program Dfragall, which was written in C and is described in Section 13.6.3. Basically, a set of compounds that is maximally dissimilar from the corporate compound collection is chosen from the set of available vendor compounds. Early versions of the process relied solely on diversity-based metrics but it was found that many nondrug like compounds were identified. As a result, structural exclusion criteria were developed to eliminate compounds that were considered unsuitable for... 

Gillet, V. J. and Willett, P. (2001) Dissimilarity-based compound selection for library design. In Combinatorial library design and evaluation. Principles, software tools and applications in drug discovery, Ghose, A. K. and Viswanadhan, A. N. (eds.), Marcel Dekker, New York, pp. 379-398. 

The resulting library consisted of 250 compounds representing different compromises between the two conflicting objectives supplied. Figure 3.5 presents a plot of the Pareto-approximation proposed by the software library (circles connected by line). Each of the remaining circles represents a solution from the initial population set after the hard filtering process. The x-axis represents similarity to ER-a ligands and the -axis dissimilarity (1-similarity)... 

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