CIS 683 Object-Oriented Software Development 19. 721 .A system is decomposed into subsystems, each subsystem may in turn be decomposed into smaller subsystems.
Communication cycles can exist.
724 .One way interaction is much easier to understand, build and change than a two-way interaction. 725 .The decomposition of systems into sub- systems can be organized as horizontal layers and vertical partitions. In a layered system, .each builds in terms of the ones below it and providing the basis of implementation for the ones above it. In a closed architecture, .each layer is built only in terms of the immediate lower layer. In an open architecture .a layer can use features of any lower layer to any depth.