Functional Decomposition Diagram

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Functional Decomposition Diagram

An analyst first must understand an organization's business functions before he or she can begin developing information systems. The functional decomposition diagram (FDD) is a business planning tool that depicts the hierarchy of business functions, processes, and subprocesses within an organization that are later described in detail using process models (chapter 6). The exercise of breaking down, or decomposing, the business functions into processes makes complex systems much easier to understand and analyze.

Understand the rules and style guidelines for functional decomposition diagrams (FDDs). •Understand the process used to create FDDs.
Be able to create a Functional Decomposition Diagram.

Supplement Outline
Functional Decomposition Diagram
Reading a Functional Decomposition Diagram
Building the Decomposition Diagram
Applying the Concepts at CD Selections

Organizations perform a variety of different functions. Traditionally, managers thought of the functions of a business as departments, such as Marketing, Finance, and Accounting. However, they are beginning to view business functions as important processes that occur throughout the organization's value chain, which is the series of interdependent activities that bring a product or service to the customer. For example, value chain activities may include inbound logistics, operations, marketing and sales, and order fulfillment.

Before an analyst can plan what systems to build for the organization, it is helpful to first understand the business functions that the organization needs to perform. Then it is much easier to identify processes that occur within the business functions, and ultimately the systems that will support those processes. This is a top-down approach to systems development.

The process of starting at a high level and moving into smaller and smaller subsystems is called decomposition. The functional decomposition diagram (FDD) is a planning tool for identifying business functions and the processes that comprise them. The diagram is the starting point for more detailed process diagrams, such as data flow diagrams, which are discussed in Chapter 6. The functional decomposition diagram itself does not depict process flows, but rather the hierarchical organization of functions and the processes that they include.

In this supplement, we first explain how to read functional decomposition diagrams and describe their basic syntax. Then we describe the way in which FDDs are built: identifying the functions of the organization and identifying their respective processes.

Functional Decomposition Diagram
Reading a Functional Decomposition Diagram
Figure 1 shows a functional decomposition diagram of the Department of Motor Vehicles . Notice that it depicts a more traditional view of the organization in that the primary functions (i.e., rectangles) correspond to the departments within the DMV: Registration, Licensing, and Regulation. By examining this FDD, an analyst can understand the high-level functions that the DMV performs and the system that is needed to support each function. Take a moment and examine the diagram before reading the next paragraph. How much do you understand?

Figure 1: Department of Motor Vehicles Functional Decomposition Diagram

Most people start reading in the top center of the FDD; however, you should note that there is no particular order implied by the boxes. Instead, the FDD depicts a hierarchy whereby top-level functions are organized into decomposed functions, and then processes, and finally into subprocesses. The first item at the top of the FDD in Figure 1 is the Department of Motor Vehicles function, which represents the organization under analysis. Beneath this function are three subfunctions, which correspond to the main functional areas within the DMV. They are connected by lines (i.e., connectors)...
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