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The Dangers of Over-Engineering a Safe System

April 2013
15 pages
The Dangers of Over-Engineering a Safe System

Attempts to increase dependability of a specific component without considering the question of overall system dependability may lead to the introduction of new problems. We examine the effect on dependability of adding software error detection to a 2oo2 system, consider the benefits and adverse consequences of this addition, and suggest other approaches to improving dependability.


Two tragic corrections — About safety claims — A simple safe system — A new vulnerability — Software error detection — About the 2oo2 system — Assumptions about the memory devices — Assumptions about handling memory errors — Calculation with no software error detection — Calculation with software error detection — Summary of findings concerning software error correction — Rethinking the problem [+]

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Chris Hobbs

Chris Hobbs

Chris Hobbs is a kernel developer at QNX, specializing in "sufficiently-available" software: software created with the minimum development effort to meet the availability and reliability needs of the customer; and in producing safe software (in conformance with IEC61508 SIL3). He is also a specialist in WBEM/CIM device, network and service management, and the author of A Practical Approach to WBEM/CIM Management (2004).

In addition to his software development work, Chris is a flying instructor, a singer with a particular interest in Schubert's Lieder, and the author of several books, including Learning to Fly in Canada (2000) and The Largest Number Smaller than Five (2007). His blog, Software Musings, focuses "primarily on software and analytical philosophy".

Chris Hobbs earned a B.Sc., Honours in Pure Mathematics and Mathematical Philosophy at the University of London's Queen Mary and Westfield College.

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