Elements of Data Flow Diagrams: Process

Study Notes

A process is an activity or function performed for a specific business reason, and can be manual or computerized.
Every process should be named starting with a verb and ending with a noun, e.g., "Determine request quantity".
Process names should be short, yet contain enough information to understand their purpose.
Each process typically performs only one activity, and avoids using the word "and" in process names.
Every process must have at least one input data flow and at least one output data flow.

A data flow is a single piece of data or a logical collection of several pieces of information.
Every data flow should be named with a noun.
Data flows describe the data elements they contain.
Data flows connect processes together, with one end coming from or going to a process, and the arrow showing the direction.

A data store is a collection of data stored in some way, determined later when creating the physical model.
Every data store is named with a noun and has an identification number and description.
Data stores are the starting point for the data model and link the process model to the data model.
All data stores must have at least one input data flow, unless created and maintained by another system or on another page of the DFD.
All data stores must have at least one output data flow on some page of the DFD.

The context diagram is the first DFD in every business process model, showing the entire system in context with its environment.
All process models have one context diagram.

The level 0 diagram shows all processes at the first level of numbering, data stores, external entities, and data flows among them.
The level 0 DFD shows the major high-level processes of the system and how they are interrelated.
All process models have one and only one level 0 DFD.

Level 1 diagrams show the detailed operation of each process on the level 0 DFD.
Each process on the level 0 DFD can be decomposed into a level 1 DFD, showing its operation in greater detail.
Level 2 diagrams show the next level of decomposition for a process, breaking it down into even more detailed sub-processes.
Level 2 DFDs balance the input and output data flows with the higher-level DFDs.