  In practical situations, it is of interest to investigate computing
approximations of sets as an important step of knowledge reduction of dynamic
covering decision information systems. In this paper, we present incremental
approaches to computing the type-1 and type-2 characteristic matrices of
dynamic coverings whose cardinalities increase with immigration of more
objects. We also present the incremental algorithms of computing the second and
sixth lower and upper approximations of sets in dynamic covering approximation
spaces.
