DFD (Data Flow Diagram) in software engineering can be drawn to represent a system of different levels of abstraction. High-level DFDs are broken down into lower levels—hacking more information and functional elements. The levels in a DFD are 0, 1, 2 or more. Here, we will see mainly 3 levels in the data flow diagram, which are, 0-level DFD, 1-level DFD, and 2-level DFD.
0 Level DFD
It is also known as context diagram. It is designed as an abstract view, showing the system as a process with its relationship to external entities. It represents the entire system as a single bubble with input and output data indicated by arrows indicating incoming or outgoing.
Level -1 DFD
In 1-level DFD, the context diagram is decomposed into multiple processes. In this level, we highlight the main functions of the system and breakdown the high-level process of 0-level DFD into subprocesses.
2-level DFD goes one step deeper into parts of 1-level DFD. It can be used to plan or record the specific or necessary detail about the system’s functioning.