Engineering is the process of allocating requirements to implementable elements. System engineering is doing this for Systems. This process consists of layers of activities that starts at an abstract level ( in the problem domain) and becomes more concrete as decisions are made about the implementable elements on the way to the implementation level (of the solution domain). Once the implementable elements have been defined, system design sets the inter-connectivity of the elements.
At each step in the process, decisions are formulated and evaluated leading to narrower sets of alternatives until the full set of system requirements are addressed at a functional level. At this point the development activities are turned over to the discipline designers for module/assembly/component development.