Let me start by stating the obvious: if I can have both consistency AND correctness in my technology dealings – I’ll take it. Unfortunately, that is seldom the case. Also, some definitions are needed to properly set the context for this discussion. For consistency, the meaning is fairly straightforward:
From: answers.com
1. Agreement or logical coherence among things or parts: a rambling argument that lacked any consistency.
2. Correspondence among related aspects; compatibility: questioned the consistency of the administration’s actions with its stated policy.
3. Reliability or uniformity of successive results or events: pitched with remarkable consistency throughout the season.
Correctness, however, is not so easy to pin down. Let’s take a look at a definition of correct (as an adjective):
From: answers.com
1. Free from error or fault; true or accurate.
2. Conforming to standards; proper: correct behavior.
The problem is, correctness – like truth – is relative and not absolute. What is correct for one, may be completely incorrect for another. So the best we can hope for is that something is appropriate for a person or group at a particular time or period. Standards help a bit to settle down this variance, but they have a long, long way to go.
So, with that context established, if I had to choose between consistency and correctness, I would hands-down choose consistency. A big part of being successful on any technology project is being able to predict the outcome with some measure of accuracy – whether its knowing the effort for each code component, system upgrade, hardware device, process change, or any other work item. That predictability is directly related to the consistency of the work items that must undergo change. Whilst the correctness of the existing targets of change has some impact on the effort for change, it doesn’t come close to the impact of having to apply multiple paths of change due to inconsistent target implementations.
Another aspect to consider is the consistency of the solution, as compared to the correctness of individual elements of the solution. An extensive amount of effort may be exerted in order to find and implement the correct individual solutions for each target of change, which can be of little benefit – or even be a detriment – to the successful and timely completion of a technology project. Often it is best to have an overall solution that is consistent across all or most targets, but may not be necessary totally correct for all targets of change.