Structural Engineering and Software: Certainty,Uncertainty and Probability

The design of any engineering artefact for use in a safety critical application should be subject to safety analysis; this applies inter alia to physical structures and software. It is often stated that software is different to other engineered artefacts because it does not degrade in any physical sense, with use or the passage of time, and it is prone to design error much more than physical systems, as much of the complexity in a system often ‘resides’ in the software. However, in assessing software and physical structures one has certainty on some issues, but there is a need to deal with probability and uncertainty with regard to others. The aim of this paper is to draw out the analogies and distinctions between the software and structural engineering disciplines, focusing on certainty, uncertainty and probability in the assessment process.