Abstract: Covering-based rough sets were studied through graphs and matrices．Firstly,bipartite graphs associated with a covering were proposed,and any two of them are isomorphic．Then a type of covering-based lower and upper approximation operators were represented through a bipartite graph associated with a covering．Secondly,the definition of 2-part matrix was presented for bipartite graphs．According to a 2-part matrix of a bipartite graph associated with a covering,not only one can know whether the covering is unary,but also reducible elements of the covering can be obtained．Finally,some characteristics of 2-part matrices of a bipartite graph associated with a partition were studied.

Key words: Covering-based rough set,Approximation operator,Unary covering,Reducible element,Bipartite graph,2-part matrix