Flow Diagrams

DFD Diagram - The Ultimate Designer's Tool

To put it in simple words, a data flow diagram or DFD diagram is a graphic pattern much like a flow chart where by the flow of data is represented with the aid of an information system. Data flow diagrams may also refer to a structured design which may be employed to visualize the processing of data. It is almost mandatory for any effective designer to first prepare a context level data flow diagram which will demonstrate the interaction that takes place between the system and the several external entities of information, that are located outside the system. This context level DFD is only the primary step. This structured design is then made to 'explode', so to say technically, in order to display the detailed picture of the system that is actually being modeled. SSADM (Structured System Analysis and Design Method) has three key components. DFDs form one of them. It is effective to both the system producers and the end users.

There are four basic components of a DFD diagram. They are: external entities or terminators, processes, data stores, and flow of data. The terminators or external entities of information are not integral parts of the DFD. They are also referred to a sinks and help in identifying wherefrom the information are coming and whereto are they going. That is, they track the in coming and out going of the flow of data. The processes assist in matters of modification of the inputs so that there are effective output generations. Data stores, as the term suggests, are places in the DFD where the data is stored. From a DFD it won't be possible to say about the relative timing that the processes undergo. Hence, data may remain accumulated in the data store for a period as long as one year. Then it is finally employed for the purpose of annual accounting. Data flow is a very functionary element among the DFD components. It reflects on the way in which data moves among the terminators, processes, and the data stores. One thing to be noted at this point: IO or Input Output Descriptions refers to such data that transgress the boundary of the system.

There are two principal approaches in which a DFD can be designed or developed. They are the top-down approach and event partitioning approach. In the former case, the designer first develops a context level DFD that shows the interaction of the data flow between the system and the system environment. The system then is zeroed down to lower level DFD. It involves a group of processes, data stores and a flow of data that occurs between the data stores and the processes. Each such process is then zeroed down to even lower levels and thus finally the DFD is reached at.

The event partitioning approach involves the listing of all the events as the primary step. A process then is constructed for each such event. Each of the processes in turn is linked to other processes with the aid of data stores. Outgoing flow of data is designed to finally draft the entire DFD.

You can do a search online to find plenty data flow diagram examples if you need to get a visual representation of DFD. note that most DFD software vemdors will have at least one data flow diagram example on their promotional material.

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