Since a locally finite topological structure plays an important role in the
fields of pure and applied topology, the paper studies a special kind of
locally finite spaces, so called a space set topology (for brevity, SST) and
further, proves that an SST is an Alexandroff space satisfying the separation
axiom T0. Unlike a point set topology, since each element of an SST is a
space, the present paper names the topology by the space set topology.
Besides, for a connected topological space (X,T) with |X| = 2 the axioms
T0, semi-T1/2 and T1/2 are proved to be equivalent to each other.
Furthermore, the paper shows that an SST can be used for studying both
continuous and digital spaces so that it plays a crucial role in both
classical and digital topology, combinatorial, discrete and computational
geometry. In addition, a connected SST can be a good example showing that
the separation axiom semi-T1/2 does not imply T1/2.