  Using the notion of cyclically pure injective modules, a characterization for
rings which are locally valuation is established. As applications, new
characterizations for Prufer domains and pure semi-simple rings are provided.
Namely, we show that a domain R is Prufer if and only if two of the three
classes of pure injective, cyclically pure injective and RD-injective modules
are equal. Also, we prove that a commutative ring R is pure semi-simple if and
only if every R-module is cyclically pure injective.
