Data flow models

Data-flow models are an intuitive way of showing how data is processed by a system.
At the analysis level, they should be used to model the way in which data is
processed in the existing system. The use of data-flow models for analysis became
widespread after the publication of DeMarco's book (DeMarco, 1978) on structured
systems analysis. They are an intrinsic part of structured methods that have been
developed from this work. The notation used in these models represents functional
processing (rounded rectangles), data stores (rectangles) and data movements
between functions (labelled arrows).
Data-flow models are used to show how data flows through a sequence of processing
steps. For example, a processing step could be to filter duplicate records in
a customer database. The data is transformed at each step before moving on to the
next stage. These processing steps or transformations represent software processes
or functions when data-flow diagrams are used to document a software design.
However, in an analysis model, people or computers may carry out the processing.
A data-flow model, which shows the steps involved in processing an order for
goods (such as computer equipment) in an organisation,
This particular model describes the data processing in the Place equipment order activity in the overall process model The model shows how
the order for the goods moves from process to process. It also shows the data stores
(Orders file and Budget file) that are involved in this process.
Data· flow models are valuable because trciCking arid documenting how the data associated
with a particular process moves through the system helps analysts understand
what is going on. Data-flow diagrams have the advarltage that, unlike some other modelling
notations, they are simple and intuitive. It is usually possible to explain them to
potential system users who can then participate in validating the analysis.
In principle, the development of models such as data-flow models should be a
'top-dovm process. In this example, this would imply that you should start by analysing
the overall procurement process. You then move 011 to the analysis of sub-processes
such as ordering. In practice, analysis is never like that. You learn about several
levels at the same time. Lower-level models may be developed fIrst and then abstracted
to create a more general model.
Data·flow models show a functional perspectivl~ where each transfonnation represents
a single function or process. They are particularly useful during the analysis
of requlrements as they can be used to show end-to-end processing in a system.
That is, they show the entire sequence of actions that take place from an input being
processed to the corresponding output that is the system's response.