Elements of Data Flow Diagrams: Process

Elements of Data Flow Diagrams

• 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.

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.

Data Store

• 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.

Context Diagram

• 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.

Level 0 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 and Level 2 Diagrams

• 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.