On commutative P. P. rings

The purpose of this paper is to study further the ideal and module structure of a commutative ring with identity, in which every principal ideal is projective. Results concerning particular modules being projective are also obtained, e.g. if R is a commutative ring with identity, then Z R (R R ) = 0 and every finitely generated nonsingular i?-module is projective if and only if R is semihereditary and K, the classical ring of quotients of R, is selfinjective.