In the Functional Model, software converts information. and to accomplish this, it must perform at least three common tasks- input, processing and output. When functional models of an application are created, the software engineer emphasizes problem specific tasks. The functional model begins with a single reference level model (i.e., be manufactured). In a series of iterations, more and more functional detail is given, until all system functionality is fully represented.
Information is converted because it flows from a computer-based system. The system takes input in various forms; Hardware, software, and human elements are applied to replace it; And produces in various forms. The transformation (s) or function may be composed of a single logical comparison, a complex numerical method, or a rule- the invention approach of an expert system. The output can light an LED or provide a 200 page report. Instead, we can create a model or flow model for any computer- based system, regardless of size and complexity.
Structural analysis started as an Information Flow Modeling technique. A computer-based system can be modeled as an information transform function as shown in figure.
A rectangle represents an external unit. That is, a system element, such as a hardware, a person or another system that provides information for transformation by the software or receives information provided by the software. A circle is used to represent a process or transform or a function that is applied to data and changes it in some way. An arrow is used to represent one or more data items.
All arrows should be labeled in a DFD. The double line is used to represent data store. There may be implicit procedure or sequence in the diagram but explicit logical details are generally delayed until software design.