How do you really understand a business process? Often what the initial analysis reveals is not exactly what is required and you are flooded with change request even before the system sees the light of day. One solution to this problem is to produce a working prototype which the people can try and give feedback. One of these is the working data store approach for data warehousing project. One of the most important aspects of these projects is that the client does not have to commit huge resources to try out an approach.
Often a key user has a really neat idea on how to improve some process and embarks on a huge project. Often as the project progresses, some flaw is revealed. The most common is a lack of buy-in by some critical people. At this stage so much has been invested that cancellation is difficult if not impossible. A far better approach would have been to test the concept with a working prototype. Hopefully if the flaws will be revealed and the project can be redesigned to correct the flaws. The organization can save big money. I have been involved in many projects where at crunch time, everybody was creating all kinds of reasons why it will not work. Often it is hard to tell whether we are dealing with a lack of readiness or a design flaw.
In my experience, a production or working prototype can eliminate some of these difficulties at an earlier stage in a project. However the key designers must be willing to create an intermediate step to get the prototype working quickly.
This is an approach that we strive to use at Project X and recommend that it be considered in many projects.