DFDs contain a system boundary which contains the whole "system". Data flows can cross that boundary into the "environment". Objects outside the system known as "terminators".

An Information System is only part of a human system. There must be a limit regarding what data it processes otherwise it will continually expand, never being a finished and complete system. This can lead to problems in the operation of the system as it becomes more complex and the probability of large system errors being introduced increases. Data stored about objects or people should only be relevant data.

When developing a system a statement of purpose must exist. This is simply a short concise statement about the purpose of system. For clarity, this may also include what is NOT to be included in the system.

The Context Diagram which is the Topmost DFD (level 0) has one process only and shows the inputs and outputs of the system.

Within stores, the structure of the data has to be described. This can be done using UML and Class Diagrams. These involve the representation of simple classes (by a rectangle) and Associations (lines) drawn between them that show what type of relationship is involved.

Cardinality describes the number of classes associated with another class. The cardinality is shown by numbers written above the association lines near the class.

DFD Elements

Processes transfom data.

Stores retain data until needed. They are usually named after the data entity.

Terminators (or entities) can represent customers or people etc... within a system.

Data Flows are instantaneous and the names of the flows are typically listed in the data dictionary along with information about each one.

Try a Computer Systems Quiz in the Computing Students Computing Quizzes Section to test your knowledge.

Search for "Data Flow Diagrams" on: Google | Kelkoo | Amazon | eBay (UK) | eBay (US)

Search for "Data Flow Diagrams" on the rest of Computing Students: Data Flow Diagrams