  In this paper, we discuss difference labeling of some standard families of
graphs. We prove that Star, Butterfly, Bistar, umbrella and Olive tree are
difference graphs. We also introduce difference labelings for some snakes
(double triangular snake, irregular triangular snake, alternate $C_n$ snake).
Furthermore we introduce a corollary helps us to find a unique difference
labeling for the complete graph $K_3$ and all forms of difference labeling for
the Star graph. Also this corollary can be used to prove that the complete
bipartite graph $K_{2,4}$ is not a difference graph but the proof is very
lengthy.
