What is "software architecture"

n. the set of structures needed to reason about the software system

Software architecture refers to the fundamental structures of a software system, the discipline of creating such structures, and the documentation of these structures. These structures are needed to reason about the software system. Each structure comprises software elements, relations among them, and properties of both elements and relations, along with rationale for the introduction and configuration of each element. The architecture of a software system is a metaphor, analogous to the architecture of a building.

Software architecture is about making fundamental structural choices which are costly to change once implemented. Software architecture choices, also called architectural decisions, include specific structural options from possibilities in the design of software. For example, the systems that controlled the space shuttle launch vehicle had the requirement of being very fast and very reliable. Therefore, an appropriate real-time computing language would need to be chosen. Additionally, to satisfy the need for reliability the choice could be made to have multiple redundant and independently produced copies of the program, and to run these copies on independent hardware while cross-checking results.

Documenting software architecture facilitates communication between stakeholders, captures decisions about the architecture design, and allows reuse of design components between projects.