In this chapter, we study problems of construction of all irreducible partial covers, all partial reducts and all irreducible partial decision rules. We describe briefly the results obtained for irreducible partial covers. Let A be a set with n elements, S be a family of m subsets of A, and t be a natural number. We consider so-called t -covers for the set cover problem (A, S). A t -cover is a subfamily of S, subsets from which cover at least n - t elements from A. A t -cover is called irreducible if each proper subfamily of this t -cover is not a t -cover. We study the problem of construction of all irreducible t -covers for a given set cover problem.