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Data Flow Diagrams Symbols
There are some symbols that are
used in the drawing of business process diagrams (data flow diagrams). These
are now explained, together with the rules that apply to them.
in general are usually designed using simple symbols such as a rectangle, an
oval or a circle depicting a processes, data stored or an external entity,
and arrows are generally used to depict the data flow from one step to
A DFD usually comprises of four components. These four components
can be represented by four simple symbols. These symbols can be explained in
detail as follows: External entities (source/destination of data) are
represented by squares; Processes (input-processing-output) are represented
by rectangles with rounded corners; Data Flows (physical or electronic data)
are referred to by arrows; and finally, Data Stores (physical or electronic
like XML files) are presented by open-ended rectangles.
data flow diagram software
Data flow diagrams present the logical flow of
information through a system in graphical or pictorial form. Data flow
diagrams have only four symbols, which makes it useful for communication
between analysts and users. Data flow diagrams (DFDs) show the data used and
provided by processes within a system. DFDs make use of four basic symbols.
Create structured analysis,
information flow, process-oriented, data-oriented, and data process diagrams
as well as data flowcharts.
An external entity is a source or destination of a
data flow which is outside the area of study. Only those entities which
originate or receive data are represented on a business process diagram. The
symbol used is an oval containing a meaningful and unique identifier.
A process shows a transformation or manipulation of
data flows within the system. The symbol used is a rectangular box which
contains 3 descriptive elements:
Firstly an identification number appears in the
upper left hand corner. This is allocated arbitrarily at the top level and
serves as a unique reference.
Secondly, a location appears to the right of the
identifier and describes where in the system the process takes place. This
may, for example, be a department or a piece of hardware. Finally, a
descriptive title is placed in the centre of the box. This should be a
simple imperative sentence with a specific verb, for example 'maintain
customer records' or 'find driver'.
A data flow shows the flow of information from its
source to its destination. A data flow is represented by a line, with
arrowheads showing the direction of flow. Information always flows to or
from a process and may be written, verbal or electronic. Each data flow may
be referenced by the processes or data stores at its head and tail, or by a
description of its contents.
A data store is a holding place for information
within the system:
It is represented by an open ended narrow rectangle.
Data stores may be long-term files such as sales ledgers, or may be
short-term accumulations: for example batches of documents that are waiting
to be processed. Each data store should be given a reference followed by an
A resource flow shows the flow of any physical
material from its source to its destination. For this reason they are
sometimes referred to as physical flows.
The physical material in question should be given a
meaningful name. Resource flows are usually restricted to early, high-level
diagrams and are used when a description of the physical flow of materials
is considered to be important to help the analysis.
It is normal for all the information represented
within a system to have been obtained from, and/or to be passed onto, an
external source or recipient. These external entities may be duplicated on a
diagram, to avoid crossing data flow lines. Where they are duplicated a
stripe is drawn across the left hand corner, like this.
The addition of a lowercase letter to each entity on
the diagram is a good way to uniquely identify them.
When naming processes, avoid glossing over them,
without really understanding their role. Indications that this has been done
are the use of vague terms in the descriptive title area - like 'process' or
The most important thing to remember is that the
description must be meaningful to whoever will be using the diagram.
Double headed arrows can be used (to show two-way
flows) on all but bottom level diagrams. Furthermore, in common with most of
the other symbols used, a data flow at a particular level of a diagram may
be decomposed to multiple data flows at lower levels.
Each store should be given a reference letter,
followed by an arbitrary number. These reference letters are allocated as
'D' - indicates a permanent computer file
'M' - indicates a manual file
'T' - indicates a transient store, one that is deleted after processing.
In order to avoid complex flows, the same data store
may be drawn several times on a diagram. Multiple instances of the same data
store are indicated by a double vertical bar on their left hand edge.
Relative Data Flow Diagram Resource
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