Software is very important to computing, and software architecture, as an aspect of software engineering and the design and construction of working computer systems, is a central concern to computer science and information technology. However, there unfortunately is not a single universally accepted definition for what software architecture itself is! Authors have used the term in various related but distinct ways. An important definition among these is that by Booch, Rumbaugh, and Jacobson, the "Three Amigos" of software engineering: "An architecture is 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 elements into progressively larger subsystems, and the architectural style that guides this organization--these elements and their interfaces, their...