The theory of systems over monoids has been investigated over than four decades. From the other side such algebraic structures endowed with orders, have been investigated as a generalization of systems, which the class of such algebraic structures together with order and monoid action preserving mappings constitutes a category. The main issue in this thesis concentrates on flatness properties of indecomposable S-posets for a monoid S, in particular cyclic S-posets. In short, in this thesis we present homological classification of monoids according to the flatness properties of indecomposable S-posets.