Basics of system modelling in UML

Everyone knows what engineering is. All that's left is to define systems, and I'm not fool enough to do that.

Some engineering artifacts are most easily analysed, described, or designed as an assembly of simpler parts. Artifacts of this kind are called systems. Some systems have the property that flowing through them are streams of some 'working fluid' (which may be matter, energy, or information), in such a way that the 'working fluid' passes in turn through many parts of the system, which is in consequence termed a sequential (or flow) system. Examples are a chemical plant, an electrical power distribution network, a digital computer, a sewer system. Systems which do not have this property are termed associative systems of which examples are a motor car, an aircraft, or a bridge - - it is with (sequential) systems that the theory of system design has primarily been developed.

When a system is brought before the public, professing to be new, and claiming to be considered as peculiarly useful, it is incumbent on those who introduce it, to show in what respects it is original, and why it is an improvement.