DFD.pptx
- 1. DATA FLOW DIAGRAM Noman Yousaf
- 2. What is a data flow diagram? • A data flow diagram shows the way information flows through a process or system. It includes data inputs and outputs, data stores, and the various subprocesses the data moves through. DFDs are built using standardized symbols and notation to describe various entities and their relationships. • Data flow diagrams visually represent systems and processes that would be hard to describe in a chunk of text.
- 3. Symbols and Notations Used in DFDs • Two common systems of symbols are named after their creators: Yourdon and Coad Gane and Sarson
- 4. Symbols and Notations Used in DFDs • One main difference in their symbols is that Yourdon-Coad use circles for processes, while Gane and Sarson use rectangles with rounded corners. There are other symbol variations in use as well, so the important thing to keep in mind is to be clear and consistent in the shapes and notations you use to communicate and collaborate with others.
- 5. Symbols • External entity: an outside system that sends or receives data, communicating with the system being diagrammed. They are the sources and destinations of information entering or leaving the system. They might be an outside organization or person, a computer system or a business system. They are also known as terminators, sources and sinks or actors. They are typically drawn on the edges of the diagram. • Process: any process that changes the data, producing an output. It might perform computations, or sort data based on logic, or direct the data flow based on business rules. A short label is used to describe the process, such as “Submit payment.”
- 6. Symbols • Data store: files or repositories that hold information for later use, such as a database table or a membership form. Each data store receives a simple label, such as “Orders.” • Data flow: the route that data takes between the external entities, processes and data stores. It portrays the interface between the other components and is shown with arrows, typically labeled with a short data name, like “Billing details.
- 8. DFD rules and tips • Each process should have at least one input and an output. • Each data store should have at least one data flow in and one data flow out. • Data stored in a system must go through a process. • All processes in a DFD go to another process or a data store.
- 9. DFD levels and layers: • DFD Level 0 is also called a Context Diagram. It’s a basic overview of the whole system or process being analyzed or modeled. It’s designed to be an at-a-glance view, showing the system as a single high-level process, with its relationship to external entities. It should be easily understood by a wide audience, including stakeholders, business analysts, data analysts and developers.
- 11. • DFD Level 1 provides a more detailed breakout of pieces of the Context Level Diagram. You will highlight the main functions carried out by the system, as you break down the high-level process of the Context Diagram into its subprocesses.
- 13. DFD levels and layers • DFD Level 2 then goes one step deeper into parts of Level 1. It may require more text to reach the necessary level of detail about the system’s functioning.
- 15. DFD levels and layers • Progression to Levels 3, 4 and beyond is possible, but going beyond Level 3 is uncommon. Doing so can create complexity that makes it difficult to communicate, compare or model effectively.
- 16. Logical DFD vs. Physical DFD • These are the two categories of a data flow diagram. • A Logical DFD visualizes the data flow that is essential for a business to operate. It focuses on the business and the information needed, not on how the system works or is proposed to work. • However, a Physical DFD shows how the system is actually implemented now, or how it will be. For example, in a Logical DFD, the processes would be business activities, while in a Physical DFD, the processes would be programs and manual procedures.