The levels of architecture per OMB (December 2006 FEA Practice Guidance)
The Clinger Cohen Act of 1996 (CIO Act) establishes the mandatory requirement for every US federal government agency to have an "IT Architecture". This followed commercial best practices. OMB has helped to define "IT architecture" by defining three levels. These levels should be applied to all applications of architecture related to federal government operations and consulting, state/local government operations and consulting, and commercial industry where clarification or differentiation is required.
Briefly, Enterprise Architecture is concerned with translating business strategy into action; EA surveys the current policy, structure, process, assets and tools, plans for future of these and identifies a transition plan (also called a "roadmap" or "sequencing plan" by various authors) . Segment architecture is concerned with "transformation of government" or "business process reengineering", dividing the enterprise into "segments" or "lines of business", "product lines" etc. to accomplish this goal. Solutions architecture or system architecture is concerned with individual systems and is the domain of system integrators and system engineers. Below these levels are constituent architecture practices such as software architecture (including OOA and OOD), data architecture, network architecture, business architecture (business analysis), hardware architecture. These may also have transformation plans that are a part of the total picture (ie "technology roadmap").
All IT architecture practice involves adding rigor and standardized practices to the management of technology and/or the use of these. This rigor and standardized practice is contained in what are called "frameworks". Different frameworks may have very different scope and purpose. Some apply to different levels, some are mainly commercial or military or some domain of activity, some measure EA activity reflectively, some provide standard taxonomies (classification systems). Some add visual artifacts (DODAF) and some do not require visual artifacts (Zachman).
"If you do anything long enough, you eventually get good at it." MK
