Dependencies are about avoiding re-inventing the wheel - software applications will have many tasks shared in common and rather than write the coding many times for each package they share libraries of commonly used functions or routines. On a Microsoft platform these routines (called run-time libraries or dynamic link libraries - file extension "DLL") are often a part of the op sys and where they are not are likely to be part of the installation package. Linux similarly share routines and uses a setup called "repositories" to resolve dependencies but they can be a problem when A is dependent on B, then B is dependent on C . . . and so one causing chains of dependencies. It is quite a complex issue as different versions of routine can cause potential conflict and when an application is uninstalled there needs to be checks in place to determine if a dll it used is now redundant or if it is still required by some other application.
