$$ A data flow diagram can be used to illustrate a system with various levels of abstraction$.$

$$ Three DFD levels are utilized, namely, level $0$ DFD$,$ level $1$ DFD$,$ and level $2$ DFD$.$

$$ The level $0$ DFD presents the system as a single process with its relationships to external entities.

$$ The level $0$ DFD represents the system at the abstraction level.

$$ The level $0$ DFD is also referred to as a context diagram since it is a specialized version of a context diagram.

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