Designing for Data Flow Diagram

This section explains the DFD's objects and how to design each object in the PowerDesigner Business Process Model.

You design Data Flow Diagram objects using business process diagram objects with a specific stereotype.

• Process
  A process is an activity, which transforms and manipulates input data to produce output data.
• Flow
  A flow conveys data between processes, external entities, and data stores. It represents data in motion, which can be computerized components, such as messages or bits, or non-computerized components, such as eggs or cake for example.
• Data Store
  A data store is the location where data resides permanently or temporarily. It responds to requests for storing and accessing data, but cannot initiate any actions. It represents data at rest, which can be computerized components, such as files or databases, or non-computerized components, such as names and addresses in an address book for example.
• External Entity
  An external entity sends or receives data from the system. It can represent a person, a machine, an organization etc., that is external to the system being modeled. Flows outgoing from external entities go to processes.
• Split/merge
  A split/merge allows you to either splits a flow into several flows so that it can send data to different destinations, or merges flows from different sources into one flow.
• Process and Data Store Numbering
  Process and data store numbering is a convenient way of referencing processes and data stores in a DFD. For example, in a lively discussion about processes or data stores in a DFD it is easier to mention a process or a data store by its number instead of its name, which can sometimes be long or complex.
• Data Flow Diagram Balancing
  The concept of balancing states that all the incoming flows to a process and all the outgoing flows from a process in the parent diagram should be preserved at the next level of decomposition.