4.3.1 Software design is the process of defining the software architecture, components, modules, interfaces, and data for a software system to satisfy specified requirements. The software architecture is the fundamental organization of a system embodied in its components, their relationships to each other and the environment, and the principles guiding its design and evolution. The software architectural design is concerned with creating a strong overall structure for software entities that fulfill the allocated system and software-level requirements. Typical views captured in an architectural design include the decomposition of the software subsystem into design entities, computer software configuration items, definitions of external and internal interfaces, dependency relationships among entities and system resources, and finite state machines. The design should be further refined into lower-level entities that permit the implementation by coding in a programming language. Typical attributes that are documented for lower-level entities include the identifier, type, purpose, function, constraints, subordinates, dependencies, interface, resources, processing, and data. Rigorous specification languages, graphical representations, and related tools have been developed to support the evaluation of critical properties at the design level. Projects are encouraged to take advantage of these improved design techniques to prevent and eliminate errors as early in the life cycle as possible. Software, developed or purchased, has additional requirements to comply with from Section 508 of the Rehabilitation Act, as defined in NPR 2800.2.
