Data-flow diagram: Difference between revisions

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{{cleanup-date|February 2005}}

A '''data flow diagram''' ('''DFD''') is graphica graphical representation of the "flow" of data through business functions or processes. More generally, aA '''data flow diagram''' iscan also be used for the [[visualization]] of [[data processing]] (structured design). It illustrates the processes, data stores, and external entities in a business or other system and the data flows between these things. PhysicalIt is common practise for a designer to first draw a context-level DFD's representfirst physicalwhich filesshows andthe transactions,interaction orbetween whilethe logicalsystem orand conceptualoutside entities. This context-level DFD's canis bethen used"exploded" to representshow businessmore functionsdetail orof processesthe system being modelled.

In analysing a business, several sets of DFD's are drawn. Initial DFD's might model the existing system (flaws and all), while later DFD's may model a solution to the problem being analysed. For these solution DFD's a logical and physical DFD is drawn. Physical DFD's represent physical files and transactions, while logical or conceptual DFD's can be used to represent business functions or processes.

DFDs can be of an existing system, or can describe the requirements for a proposed or planned system. A DFD of an existing system should represent the functions and processes that are already in place, flaws and all. A required system DFD is a diagram of a system that will be implemented in the place of the current one.

Data flow diagrams were invented by Larry Constantine, the original developer of structured design, based on Martin and Estrin's "data flow graph" model of computation.

==Components==

TheFour components describedare orused illustratedto indevelop a DFD. shouldThese includeare:

* Data Flow (represented by an arrow)

* Data Process (represented by a circle or rounded rectangle)

* External Entity (represented by a square or oval, also called a 'Source/Sink'

* Data Store (represented by two parallel lines, sometimes connected by a vertical line)

==Data Flow==

A data flow is the core of the data flow diagram. Each data flow in the system should be unique and demonstrate data flowing between two other elements in the system. Depending on the notation used, several rules apply to data flows, such as a limitation on two-sided arrows. It is generally agreed that each data flow should be uniquely labelled in the DFD.

==Data Process==

==Data Store==

==External Entities==