A system needs to be "fit for purpose". There is no one correct design model for a system. Different analysts may draw up different models for a specified system. To be "fit for purpose" the system needs to meet the requirements specified for an ideal system.

DFDs that are drawn up need to be correct. If they have errors in them or the wrong symbols are used they are useless. Some further possible errors include:

• Data flows cannot exist between stores or terminators (processes are needed to retrieve and move the data)
• Processes must be given a number and name in the appropriate places
• Data flows must be named
• All stores must be given numbers.
• Stores should typically have an input data flow so that it can be updated as well as an output flow otherwise the data is not being used for anything
• Processes must have at least one input and one output

Successful systems development will involve breaking the system down into components or modules. If there is "low coupling" between sections or modules in a system, this means that there is little data flow between them. These sections can therefore be developed independently quite easily without large problems occuring when bringing them together to form the system as a whole.

The system's outputs must also be relevant and necessary for the user. Irrelevant and useless output creates complications.

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

Search for "Systems Development" on: Google | Kelkoo | Amazon | eBay (UK) | eBay (US)

Search for "Systems Development" on the rest of Computing Students: Systems Development