How do You Define Software Architecture?

SEI has a good material devoted to to Software Engineering. Stating with the basic question, How do You Define Software Architecture?. This page presents many classical definitions from the most known authors of Software Engineering, as well as the definitions that the comunity around the world submitted to SEI. Another must reading article is that one that defines the Duties of a Software Architecture. Let's point out some definitions:

• "The software architecture of a program or computing system is the structure or structures of the system, which comprise software elements, the externally visible properties of those elements, and the relationships among them. First, architecture defines elements. The architecture embodies information about how the elements relate to each other. This means that architecture specifically omits certain information about elements that does not pertain to their interaction. Thus, an architecture is foremost an abstraction of a system that suppresses details of elements that do not affect how they use, are used by, relate to, or interact with other elements. In nearly all modern systems, elements interact with each other by means of interfaces that partition details about an element into public and private parts. Architecture is concerned with the public side of this division; private details of elements—details having to do solely with internal implementation—are not architectural...."
• "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 collaborations, and their composition (The UML Modeling Language User Guide, Addison-Wesley, 1999)." -- Booch, Rumbaugh, Jacobson 1999
• [Lane 90]: Software architecture is the study of the large-scale structure and performance of software systems. Important aspects of a system's architecture include the division of functions among system modules, the means of communication between modules, and the representation of shared information.