Software reliability demands

Strigini, L. Bounds on survival probabilities given an expected probability of failure per demand. D1SP02 Project Technical Report LS-DISPO2-03, Centre for Software Reliability, City University London (July 2003)... 

Equipment technology and processing software for FTIR are very robust and provide a high degree of reliability. Concerns arise for only the most demanding applications. For quantitative work on an isolated feature in the spectrum, the rule of thumb is that the spectrometer resolution be one-tenth the width of the band. FTIR instruments routinely meet that requirement for solids. 

System integration involves numerous miscellaneous development activities, such as control software to address system start-up, shut-down and transient operation, and thermal sub-systems to accomplish heat recovei y, heat rejection and water recoveiy within the constraints of weight, size, capital and operating costs, reliability, and so on. Depending on the application, there will be additional key issues automotive applications, for example, demand robustness to vibrations, impact, and cold temperatures, since if the water freezes it will halt fuel cell operation. 

As with other spectroscopic techniques, UV-vis spectroscopy can readily be used in lab-based R D. The implementation as process monitors, scanning for deviations from the set state, is certainly an added value and low in maintenance requirements. UV-vis based process control is more demanding on precision, reliability, exactness and operability. The steady progress both in hardware and software is facilitating the growth of UV-vis process analytics in both the pharmaceutical and chemical industries. Given the vast increase in information and knowledge-based control, this may just be what the industries need. 

Availability, in general, is defined as the ability of the plant/equipment to perform its required function over a stated period of time. Maintainability is the probability that a failed item can be restored to operation effectiveness within a given period of time when repair action is performed as per the specified procedure (Smith, 2011). Software is available for performing RAM studies. For smaller projects, spreadsheets can be used. Reliability and process safety are interlinked, and so combined RAM and safety (RAMS) studies can be performed with the RAMS software (Sikos and Klemes, 2010). It considers many factors affecting the plant performance such as equipment performance, redundancy, demand requirements and logistics. RAM analysis is based on statistical failure data such as mean time between failures (MTBF), mean time to repair (MTTR), mean time to failure (MTTF) and mean down time (MDT). Wherever possible, failure data available within the company should be used for RAM/RAMS study. If not, typical failure data available in the literature/software can be used. 

McDonald M, Musson R, Smith R (2008) The practical guide to defect prevention - techniques to meet the demand for more reliable software. Microsoft Press Milius S, Steinke U (2010) Modellbasierte softwareentwicklung mit SCADE in der eisen-bahnautomatisierung. http //www.iti.cs.tu-bs.de/ milius/research/modelbased.pdf Accessed 24 August 2010... 

As more and more data was eolleeted, the irmovators and early adopters demanded more and more analysis so eompanies began to provide commercial systems whieh were integrated, analytieal and reliable. Software was developed to help analyse data and present the results in a user-friendly way and, during the late 1990s and up to the present day miniaturisation of hardware meant that the components were mueh easier to fit onto maehines and, as we have now, many could be earried arotmd in the hand by agronomists, just like a mobile phone. 

Safety analysis is an essential part in the development of medical devices. Safety is an essential property of the systems just like efficiency and reliability are. Some of the devices developed are life-supporting. This means that a failure of such a device may lead to the death of a patient if no adequate safety measures are applied. As complexity of the devices increases, the demand for automation in safety analysis grows. It is common sense that the traditional techniques are not necessarily complete. In addition, the results of such techniques largely depend on the experience of the analyst. Knowing that it is not sufficient to just replace the traditional manual techniques for automated counterparts, we follow a combined approach. The trend with new developments indicates a steady increase in the software portion of the systems. For some systems, the portion of total development time dedicated to hard-ware development is between 10 and 20%. This shift towards software is accompanied with an increase in the complexity of the systems. For this reason, the techniques used for safety analysis have to cope with the increased complexity. Automated tools can be effective in dealing with the inherent complexity of largely software-based systems. While for traditional techniques emphasis is placed on completeness, this changes to accuracy of the model for the automated techniques. 

Software diversity has been advocated as a means of improving the reliability of safety related software and in particular safety systems that react to a demand, where a 1 out of 2 or a 2 out of 3 voting scheme can be used to ensure that some safety action is performed. This approach is used in industry (e.g. for railway interlocking), but development and maintenance is costlier than for a non-diverse system and it is not easy to predict in advance the likely safety improvement that can be achieved. 

The second reliability target is interpreted to mean that for say every 5000 demands made upon the PLC, it is tolerable for a design error to result in one failure. As above, the number of demands is somewhat arbitrary. It is therefore claimed that 50000 demands accumulated experience should provide a sufficient basis to claim an propriate level of reliability. The period for which experience is required is some 10 times that target again as above. In this context i.e. a safety related application, a demand is a set of circumstances which require a certain specified operation from the software, which if not provided will result in a hazard. The nature of the specification implies that the demands are infrequent (in time). 

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