Here are some jewels about Software Engineering that are worth reviewing. I recommend the rest of the article. It’s an oldie but goody!
Recently I have been doing a lot of work deciphering “other people’s codeâ€. I would say the largest part of the work has been in error detection and removal. Even a seemingly comprehensive test plan does not make me terribly confident. I have been humbled by logic problems and faulty design requirements too many times.
Reliability
RE1. Error detection and removal accounts for roughly 40 percent of development costs. Thus it is the most important phase of the development life cycle.
RE2. There are certain kinds of software errors that most programmers make frequently. These include off-by-one indexing, definition or reference inconsistency, and omitting deep design details. That is why, for example, N-version programming, which attempts to create multiple diverse solutions through multiple programmers, can never completely achieve its promise.
RE3. Software that a typical programmer believes to be thoroughly tested has often had only about 55 to 60 percent of its logic paths executed. Automated support, such as coverage analyzers, can raise that to roughly 85 to 90 percent. Testing at the 100-percent level is nearly impossible.
RE4. Even if 100-percent test coverage (see RE3) were possible, that criteria would be insufficient for testing. Roughly 35 percent of software defects emerge from missing logic paths, and another 40 percent are from the execution of a unique combination of logic paths. They will not be caught by 100-percent coverage (100-percent coverage can, therefore, potentially detect only about 25 percent of the errors!).
RE5. There is no single best approach to software error removal. A combination of several approaches, such as inspections and several kinds of testing and fault tolerance, is necessary.
RE6. (corollary to RE5) Software will always contain residual defects, after even the most rigorous error removal. The goal is to minimize the number and especially the severity of those defects.
Frequently Forgotten Fundamental Facts about Software Engineering