Composed
Not only human users can interact with computer programs, but also other programs. This case occurs even much more frequently. Actually it happens all the time: a great deal of the programs running in a computer just control other programs or provide them with data or hardware resources or so.
Furthermore, every program is composed of smaller units, which themselves may be called “programs”. Each serves a certain function. When required, it gets initialized and interacts with other parts of the program by means of special channels or interfaces — which, after all, are again nothing but such sub-programs serving certain functions…