Abstract: Neighborhood system based rough set and covering based rough set arc two important expansions of the clas- sical rough set, I3y means of comparing the lower approximation sets, the upper approximation sets and accuracy meas- ures,thc relationships of neighborhood system based rough set and six covering based rough set models were systemati- cally studied. The conclusion is that the relationships between the lower or upper approximations of neighborhood sys- tem based rough set and six covering based rough set models are clear, either can be compared, or not. Under the compa- ruble situation, it was proved that there arc inclusion even equivalence relations. Under the incomparable situation, it was proved by counter-examples. The comparative study on different expansions of rough set not only provides a better un- derstanding of these models, but also gives a hand on learning rough set in the macroscopic level.

Key words: Neighborhood system based rough set, Covering based rough set, Accuracy measure, Comparison