A system is a whole, composed of a set of elements that interact in an organized way to achieve one or more defined objectives.

The purpose of a system answers the question "Why does the system have to exist?" This is the meaning, the reason of being of the system.

The mission answers the question "What does the system do?": It is the highest level function provided by the system and perceptible by its main user through the actions and reactions of the system generated from the solicitations exerted on the inputs. 

The job scenarios answer the question "How does the system ensure its mission?" And understand how it works and the interactions with the outside world and define the functions and the area of operation of the system. The job scenarios detail the mission by considering the different profiles and contexts of use and maintenance in operational condition.

From the purpose and the mission, the objectives characterize the need qualitatively and quantitatively, by measurable data:
What performance?
At what cost?
For what life time?
For which stakeholders?
In what context ?

A stakeholder is an entity concerned by the system, its design, its use, its impacts on a given context and therefore the stakeholder is likely to issue expectations or constraints on the system. Different stakeholders are involved throughout the life cycle of the system, thereby having different perspectives on the system.

Architecture is the fundamental organization of a system represented on the one hand, by its constituents, their interrelations, their relations with the environment and on the other hand by the principles guiding its conception and its evolution. The architecture of a system is a representation, at a given level of abstraction and granularity, of a system in the form of a structure identifying the constituent elements of the system and their interactions.

The context corresponds to all the circumstances in which an event occurs, is an action. The context of a system is the set of external elements that condition it, in its finality and in its operation, or even in its structure. We will also use the term employment environment. The spatial context delimits the notions of exterior and interior and borders and thus leads to notions of interface, exchanges and constraints imposed by the outside system. The environmental context imposes conditions (employment environment, available resources, economy of detention and use) that constrain the choice of the definition and the technologies used.