Graphs are widely used to model complicated data semantics
in many applications. In this paper we propose
Fast-ON, an efficient algorithm for subgraph isomorphism
problem which has proven to be NP-complete.
Fast-ON is based on Ullman algorithm [8]. It improves
the search space of Ullman algorithm by considering two
effective optimizations. Comparing to the well-known algorithms
Ullman and Vflib [3], Fast-ON achieves up to 1-3
orders of magnitude speed-up.