Projecte - Dataflow

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Introduction

The dataflow diagram is a modeling tool that allows us to picture a system as a network of functional processes, connected to one another by “pipelines” and “holding tanks” of data.

The dataflow diagram is one of the most commonly used systems-modeling tools, particularly for operational systems in which the functions of the system are of paramount importance and more complex than the data that the system manipulates.

Note

Many users will be familiar with the underlying concept of DFDs, because the same kind of notation has been used to build work-flow models of organizations.

This is important to keep in mind: DFDs can be used not only to model information-processing systems, but also as a way of modeling whole organizations, that is, as a tool for business planning and strategic planning.

Components

This figure shows a typical DFD for a small system.

Before we examine its components in detail, notice several things:

  • It hardly needs to be explained at all; one can simply look at the diagram and understand it. The notation is simple and unobtrusive and, in a sense, intuitively obvious. This is particularly important when we remember who is supposed to be looking at — not the systems analyst, but the user! If the user needs an encyclopedia in order to read and understand the model of his system, he or she probably won’t bother to do either.

  • The diagram fits easily onto one page. This means two things: (1) someone can look at the diagram without being overwhelmed, and (2) the system that is being modeled by the diagram is not very complex. What do we do if the system is intrinsically complex, for example, so complex that there would be literally hundreds of circles and lines in the diagram? We will discuss this later.

  • The diagram has been drawn by a computer. There is nothing wrong with a hand-drawn diagram, but this figure and many of the other DFDs shown in this page are drawn with the assistance of Projecte - Mermaid. This means that the diagram is likely to be drawn more neatly and in a more standardized fashion than would normally be possible in a hand-drawn diagram. It also means that changes can be made and new versions produced in a matter of seconds.

The Process

The first component of the DFD is known as a process. Common synonyms are a bubble, a function, or a transformation.

The process shows a part of the system that transforms inputs into outputs; that is, it shows how one or more inputs are changed into outputs.

The process is represented graphically as a circle, as shown in Figure 9.2(a).

Some systems analysts prefer to use an oval or a rectangle with rounded edges, as shown in Figure 9.2(b); still others prefer to use a rectangle, as shown in Figure 9.2(c). T

The differences between these three shapes are purely cosmetic, though it is obviously important to use the same shape consistently to represent all the functions in the system. Throughout the rest of this book, we will use the circle or bubble.

Pending

https://web.archive.org/web/20090410072544/http://yourdon.com:80/strucanalysis/wiki/index.php?title=Chapter_9

https://github.com/mermaid-js/mermaid/issues/1893