As mentioned in my previous blogs, Data Flow Diagrams (DFD’s) are graphical representations of the flow of data in an information system. A form of process modelling, they are made up of four main components:
Processes are jobs that are there to be done within the data. They are rectangular in shape. They transfer incoming data flows into outgoing data flows.
These are any class of people, an organization or another system that exists outside the system that interacts with the system. These are the places that provide the organisation with data sent to them by the organisation. (eg. customers, partners) These are generally oval in shape.
These mark movement in a system and can be described as a pipeline that will carry the data. These arrows connect the processes, external entities and data stores. Without data flows the DFD would have no substance.
The best description of these is data at rest. It represents holding areas for collection of data. Processes add or retrieve data from these stores. Only processes are connected to data stores.
DFD’s fit in at the Analysis and Design phase of the Software Development Life Cycle. In the analysis stage it is mainly fact finding. They investigate business processes and the current system. They help with modelling the current systems. In the Design phase, it describes how the system will fulfill the user requirements. It also looks after the modelling of the current systems.
In my next blog I will focus on the advantages of both flowcharts and data flow diagrams.
www.cathaldoyle.com– Lecture 17
The image attatched shows what a complex DFD may look like.