The intuitive appeal of object oriented programming is that it provides better concepts and tools to represent the natural structure of the real world as closely as possible. The advantages of this direct representation capability in programming and data modeling are (1) data abstraction or encapsulation, the program objects have a one to one correspondence with the problem objects, and (2) reusable toolkits with well-defined minimal interfaces. We have created classes of SepData objects for seismic data manipulation. Data are encapsulated into objects such as Cube, Plane and Trace. Graphic objects are attached to these data objects to facilitate interactive programming. This library is already used for an object-oriented implementation of the Zplane and Overlay programs.