Root Cause Analysis (RCA) is often seen as having short-term impacts, when, in fact, the returns may be long term. Understanding the differences is critical to successful implementation of RCA.
The chart below lists some of the differences between RCA in software and RCA in other disciplines. This article will address these differences and how they should shape application of RCA to software.
Items one and four are related and are sometimes misunderstood by those who initiate RCA as a "solution" to software defect prevention (using the "If we get to the root cause of critical customer problems, we can make them go away" train of thought). This confuses the physical realm with the intellectual realm. Three Mile Island, TWA 800, Challenger, and other major disasters could be analyzed to identify operational or physical failures that, once identified, could be prevented by a redesign of a part, system, or operational procedures. When people apply these methods to the software profession and expect analysis of critical problems to prevent future failures, they fail to understand the root causes of software defects.
They falsely assume that something that causes a major customer failure must somehow have been caused by a major oversight or repeatable cause, where the consequence of the fault will always be proportionate or related to the initial error. For software this is not true. Single-character coding errors caused Mariner 1 to crash into Venus and the 800 telephone system to crash back in 1994. This means that RCA of serious failures will not consistently prevent other serious failures, as the root cause of simple failures may generate serious failures in other parts of the product. A simple typographical error can have a minor impact in one case and a catastrophic failure in another case.
|Software||Other Engineering Discipline|
|1||Many failures of varying consequence||Single events with major and often catastrophic results|
|2||Failures caused by "intellectual" shortfalls||Failures caused by physical interactions or mechanical fatigue,
operational errors, management failures, or design errors
|3||Many common-cause faults||Typically unique faults|
relation of cause to failure or future failures in many cases
|Cause may repeat with similar consequence|
|5||Typically low effort per failure||Often significant effort, many times with political overtones|
|6||Prevention may be well into the future; requires investment to prevent future errors||Scapegoat and financial responsibility|
If we are lucky enough to identify a common process failure related to a specific failure mode, then RCA will have a benefit. This leads us to identifying a common cause for multiple failures, which is the third item in the tabled list. By systematically analyzing multiple failures, patterns of common cause may be identified, leading to a single fix in a requirements, design, or coding process that eliminates multiple faults with one change. A secondary impact of this item is that RCA of single failures is self-defeating, as patterns will not be apparent until multiple failures are analyzed and common causes identified. If you go back to one of the original papers on Defect Prevention and search for "Defect Prevention"), you'll find that the RCA process involves collecting data from multiple failures and analyzing them as a group.
The second item, intellectual vs. physical, is one of the reasons the first and fourth items present their difficulties. Metal fatigue, for example, can be attributed to specific causes that, once eliminated, ensure these failures will not be repeated. The human mind, however, is not so accommodating. If we look at some of the reasons errors get into software, such as communications loss, noisy work environment, multi-tasking impact