A case history analysis of software error cause-effect relationships

Where do software errors come from? Almost thirty years ago, Nakajo1991 analyzed approximately 700 software errors in four commercial measuring-control products and used a restricted version of fault tree analysis (FTA) to capture meaningful cause-effect failure patterns. The authors observed failures at chosen points along a cause-effect process of software errors; selected points are highlighted below:

1. inappropriate management of work system
2. work system flaw (process, individual, environmental flaws)
3. human error
4. program fault
5. system failure

The methodology in this paper provides a systematic way to map software failures to their ultimate cause and leverages statistical analysis to draw conclusions about rates of particular errors across projects. However, the study only analyzed two system products and two firmware products and was not able to study either individual or environmental paths along its own defined error cause-effect process.

Nakajo1991 concluded that:

1. Two major error patterns resulted from hardware or software interface misunderstandings.
2. Two more common error sources emerged from system and module function misconceptions.
3. Structured Analysis and Structured Design (SA/SD) methods were effective in mitigating the first two but not the last two sources of errors.

Thirty years is a long time in our industry, but this work shows that systematic analysis of errors, and of strategies to mitigate them, was possible long before the internet made "big data" about software available. The question the paper doesn't ask, but we should, is, "Why aren't analyses like these an everyday thing?"