When doing a needs analysis, there are many different approaches and they don't have to be mutually exclusive. You don't have to make a "Sophie's Choice" between top-down and bottom-up. It maybe a bit chaotic if you tried to do them in the same session but you can incorporate both approaches as part of an overall plan.
The BABOK 3rd edition in section 6.1.4 identifies the four different approaches of top-down, bottom-up, from middle management and from external drivers. Additionally, it mentions that "The definition of business needs is frequently the most critical step in any business analysis effort."
So lets say that you have a project where 13,000 employees from different divisions are going to use an off the shelf cloud based database tool to be used for ongoing operations and to enable corporate leadership to make business decisions based upon leveraging cutting edge business intelligence technologies.
Clearly, the top-down is the correct approach is needed because it is driven by the need for corporate leadership to make high level business decisions. Although, there is that pesky 13,000 employees using it for operational needs at a functional level.
Well, that part might be a bit muddy but clearly we can rule out the middle management option, correct? Although, we can safely assume that these 13,000 employees from a plethora of related departments may need some significant middle management support.
At least the external drivers can take a back seat correct? Except that an off the shelf solution was chosen and the vendor is the only one that can do the modifications. Based on the scope, we can assume that there are multiple external technical influences that might come to bear. How likely is the chance that someone will use the word "Mobile" somewhere in their described needs? Oh, did I forget to mention this use case is within a highly regulated industry?
This use case that I described above isn't completely fictional. In fact, it is barely fictional at all. A single approach vector cannot work here. Instead a coordinated attack from different angles is the only approach that will likely meet the majority of business analysis needs for the above use case.
Let the fun begin, eh?
©2015 Dwayne Wright