Data Flow Diagram
The Data Flow Diagram (DFD) serves as a critical tool in understanding how data moves through various processes and systems in an organization. It delineates the sources, transformations, and destinations of data. Here are its core components:
Components:
External Entities: These are the actors or systems that interact with the process but lie outside the defined system's boundary. They are generally represented as boxes.
Processes: Indicated typically by circles, these are the functional units that transform incoming data flow into outgoing data flow. They describe what the system does with the data.
Data Stores: Represented as two parallel lines, these indicate where data gets stored. It could be a database, a physical storage, or an electronic storage medium.
Data Flow: Arrows show the direction of data movement. They can indicate data moving to and from processes, data stores, and external entities.
Usage:
Data Flow Diagrams are typically developed during the analysis phase after initial models like Entity Relationship Diagrams and process flows have been established.
The diagram helps to understand the flow of data between systems and actors and is particularly useful for visualizing data inputs and outputs for each process involved.
It does not indicate the timing, sequence, or the control factors affecting the data flow, only the stateless flow of data itself.
Relationship to Requirements:
The diagram is not usually used as a stand-alone requirements document but rather complements the requirements by providing a visual representation of data movements, which helps in understanding how the requirements will be fulfilled.
The business data objects and processes shown in the DFD can be traced back to the requirements. It serves as a helpful tool to stakeholders and developers for understanding how data requirements are met and how data flows through the system.
This contextual understanding leads to the identification of specific data requirements and constraints, thereby facilitating a more nuanced and complete requirements gathering process.
By using a Data Flow Diagram, you can provide all stakeholders, including both technical and business team members, with a clear, unambiguous representation of how data moves within the system. This aids not only in requirements gathering but also in the design and implementation phases.