| Dependable Pervasive Systems (2004) | |||||||||||||||
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| This document therefore concentrates on the problems of dependably producing large complex distributed systems to match their specifications within time and budget constraints, and the problems of actually achieving adequate operational dependability from such systems when they are deployed. 3. Such systems will often be constructed out of multiple pre-existing systems and need to be highly adaptable. Most will embody human beings as, in effect, system "components." The successful design and deployment of such systems is a major challenge, and calls for socio-technical as well as technical dependability expertise. Interdisciplinary approaches are essential. 4. Dependability (also termed "trustworthiness") is the ability to avoid failures that are more frequent or more severe, and outage durations that are longer, than is acceptable - the causes of such failures are termed faults. The four basic dependability technologies are (i) fault prevention (to avoid the occurrence or introduction of faults), (ii) fault removal (through validation and verification) and (iii) fault tolerance (so that failures do not necessarily occur even if faults remain), the effective combination of which is crucial, together with (iv) fault forecasting (the means of assessing progress towards achieving adequate dependability). 5. A variety of fault prevention and fault removal techniques are in use, in some cases as part of a formal (mathematically-based) design method -- however, there is a need to make such methods and their tools easier to use. Fault tolerance is very effectively used for hardware faults, and in some arenas for software faults. Fault forecasting (i.e. system evaluation, involving estimation of the number and likely consequences of any remaining faults) can be quite effective,... | |||||||||||||||
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