Software does not wear out but it does fail and most failures are due to specification errors and code errors with only a few errors in copying or use. The only software repair is by reprogramming and adding safety factors is almost impossible. Software reliability improves by finding errors and fixing the errors but estimating the number of errors which canse failures is extremely difficult as many branches of software code may lie dormant and unused until special events occur to make the latent failures obvious. Software failures are not often time related but are more software code page dependent. Software reliability is improved by extensive testing to disclose the failures and then fixing them to repeat the test all over again to validate the fix did not generate more failures and to continue the search of other latent defects.
Why: More than 50% of the software bugs (failures) occur from specifications with lesser amounts of failures from system design and the coding process and this is due to the lack of visibility in the software process along with problems from those specifying the requirements with problem roots in ambiguities, inconsistencies, incomplete statements, and lack of logical requirements. This requires that both inputs and outputs for software must be specified in greater detail than for mechanical, electrical, or system data to avoid the errors and conflicts.
When: “Clean room” software procedures are a technique for extracting details from the customers to insure the programmers and they are used up-front to reduce errors and wasted code. The acquiring of the data is tedious and roughly 80% of the software budget is spent get the details “right” before programming commences.
Where: Disciplined software specialist carefully work the plan up-front to reduce errors and testing time. Undisciplined, so called “neo-experts” want to see busyness in code writing up-front and thus their software reliability is worse from not having a firm foundation from which to work.
These definitions are written by H. Paul Barringer and are also posted on his web site at www.barringer1.com
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