The set of significant decisions about the organization of a software system, the selection of the structural elements and their interfaces by which the system is composed, together with their behavior as specified in the collaborations among those elements, the composition of these structural and behavioral element into progressively larger subsystems and the architectural style that guides organization: these elements and their interfaces, their collaborations, and their composition.
-Verhoff
The software architecture of a deployed software is determined by those aspects that are the hardest to change.
