……………………………………………….Expertise in .NET Technologies

Introduction to Data Flow Diagrams

Posted by Ravi Varma Thumati on December 6, 2010

Data flow diagrams are useful in modeling high-level systems and processes.  These diagrams show the way in which data flows between elements in a system and between the system and external entities.

Typically, several data flow diagrams are used to understand a problem.  The top-level diagram is called a context diagram and contains one Functional Transform which represents the entire system.  The context diagram also shows the external entities that interact with the system.  The following context diagram shows an order entry system that interacts with customers and shippers.  The solid lines represent the flow of data.

Data flow diagrams in Visual Case can model the flow of control as well as the flow of data.  You can easily show and hide the control transforms and control signals on your diagrams at any time.  A Control Transform can be decomposed into a State Diagram.  Together, the state diagram and control transform model the dynamic aspects of the system.

Visual Case provides you with the following objects with which to build data flow diagrams:

The external entities are the sources and destinations of a system’s input and output.  They are objects that are not within the system, but with which the system interacts.
Data storages represent entities in the system in which data is stored.  Examples include databases and files.
A functional transform represents an action taken on the data.  This may include a calculation, conversion, or other task performed.
A control transform can send and receive control signals that help to explain the control over the data flowing through the system.  In Visual Case you can optionally show and hide this flow of control at any time.
Notes are used to add a description on the diagram for an object.  In Visual Case, you can connect a note to any object using a note link.
Data flows represent the movement of information through the system.  Control signals connect control transforms to other objects on the diagram and represent control over the data.

In Visual Case, you can label data flows and control signals with any text that you like.  You can also choose between three styles of link: segmented, direct and quadratic (shown from top to bottom respectively).

You can also select to show arrows at either, both or neither ends of a link.

Example of a Data Flow Diagram

Above is an example of a data flow diagram created with Visual Case.  Some important things to note are:

  • The two links labelled “Student Information” have been mapped to the same data flow.  If you change the name of one, the other will automatically change.  Most objects in Visual Case can easily be mapped to other entities
  • The processes are all high level tasks that could be exploded into sub-data flow diagrams that clarify and further specify the task
  • The data flows are all labeled with the information that is being transferred

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