A Focus on Data
|Data flow diagrams (DFDs)
Common DFD mistakes
Data flow diagrams can assist in
We will discuss building data flow diagrams in class in some detail, particularly issues which have not been included here, such as leveling and context diagrams. During and following those discussions I hope that these pages will provide a useful reference for building useful and effective DFDs. While no substitute for disciplined software engineering training, the ideas expressed here can provide a useful introduction to the subject, especially when combined with prototyping software that understands data flow and data structure concepts.
Leveling refers to using multiple pages to show data flows at varying levels. For example, one page of a DFD might show processing steps 1.0, 2.0, and 3.0. A second page might show the subprocesses within step 1.0: it would have the same total inputs and outputs as 1.0, but would show an additional level of detail in describing processing steps 1.1, 1.2, and 1.3 that make up process 1.0. A third page might show steps 2.1, 2.2, and 2.3; a fourth page steps 3.1, 3.2, 3.3, and so on.
Context diagrams offer a way to describe the scope of a DFD by identifying (at its highest level) the boundaries of the system. The context diagram shows all the sources and sinks for the business process, a summary of its highest level processing steps, and a summary of its main data stores.
We will work with these ideas more in class. Good luck.
@ 1999 Charles Osborn