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Functional Decomposition Overview

Getting ready to create a Functional Decomposition Diagram (FDD)

During Requirements Modeling of the Analysis Phase it may be helpful to model the business functions and processes as they currently are. One way to do this is to create a Functional Decomposition Diagram (FDD). This top-down planning approach attempts to gain a broad understanding of the informational needs of the entire organization. In contrast to the top-down planning approach, a bottom-up planning approach requires the identification of business problems and opportunities that are used to define projects. The bottom-up approach often fails to view the informational needs of the entire organization. This can result in the creation of disparate information systems and databases that are redundant or not easily integrated without substantial rework.

A FDD is a snapshot of the business functions and processes as they currently are, before any changes are envisioned or implemented. It is an iterative process of breaking the description of a system down into finer and finer detail. The system is comprised of functional business areas, which are composed of a mix of other lower-level functional business areas and/or business processes. Typically, the chart will appear as an inverted tree with the system as the ‘root’, business functional areas as the ‘branches’, and business processes as the ‘leaves’.