Data flow diagram A data flow diagram (DFD) is a graphical
representation of the "flow" of data through an information
system, modeling its process aspects. Often they are a
preliminary step used to create an overview of the system which
can later be elaborated. DFDs can also be used for the
visualization of data processing (structured design). A DFD
shows what kinds of information will be input to and output from
the system, where the data will come from and go to, and where
the data will be stored. It does not show information about the
timing of processes, or information about whether processes will
operate in sequence or in parallel (which is shown on a
flowchart). It is common practice to draw the context-level data
flow diagram first, which shows the interaction between the
system and external agents which act as data sources and data
sinks. On the context diagram the system's interactions with the
outside world are modelled purely in terms of data flows across
the system boundary. The context diagram s