1.What is the DFD Context Diagram?
-This is the first level of the DFD.
-In the context diagram, we just visualize the data flow between the data source and the system (0)

2.Element of DFD Context Diagram
2.1 The System
-The system is visualized as rounded rectangle
-We have the number 0 denoted on the top and follow by the name of the system in the next line
2.2 Data Source
-The data source is visualized as non rounded rectangle
-The data source is usually as a person or an entity where the data initialize
2.3 Data
-This is the data flow from/to data source to the system 0.

3.Relationship
-We draw arrow to indicate the data flow between the system 0 to the data source
-The data can be from the data source to the system OR the system return the data to data source
-We need to clearly define the data that is transferred in the arrow

4.Step to draw a DFD Context Diagram
-List the system 0
-List all of the data source
-Draw the flow and indicate the data

App A: Note
-The data must be N/N Phrase
-The is no inflow or outflow constraint for data source and system 0 at this context level 0 diagram

App: Sample
https://prestobear.com/2018/05/case-study-mortgage-rate-quote-system/