TABLE C-1 Hierarchy of Systems Components

Term

Definition

System of systemsa

A configuration of systems in which component systems can be added or removed during use, each providing useful services in its own right, and each is managed for those services. Yet together they exhibit a synergistic, transcendent capability.

Systemb

An integrated set of elements, segments, and/or subsystems that accomplish a defined objective, such as an air transportation system.

Subsystemb

An integrated set of assemblies, components, and parts that performs a clearly separate function, involving similar technical skills, or a separate supplier. Examples are an aircraft onboard communications subsystem or an airport control tower as a subsystem of the air transportation system.

Assemblyb

An integrated set of components and/or subassemblies that constitute a defined part of a subsystem, e.g., the pilot’s radar display console on the fuel injection assembly of the aircraft propulsion subsystem.

Subassemblyb

An integrated set of components and/or parts that comprise a well-defined portion of an assembly, e.g., a video display with its related integrated circuitry of a pilot’s radio headset.

Componentb

Composed of multiple parts; a clearly identified item, e.g., a cathode ray tube or the ear piece of the pilot’s headset.

Partb

The lowest level of separately identified items, e.g., a bolt to hold a console in place.

aAir Force Scientific Advisory Board, 2005, System-of-Systems Engineering for Air Force Capability Development, SAB-TR-05-04, July. Available at http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA442612. Last accessed on April 2, 2007.

bInternational Council on Systems Engineering (INCOSE), 2004, INCOSE Systems Engineering Handbook (Version 2A), Seattle, Wash.: INCOSE.

maintainability, supportability, global flexibility, scalability, interoperability, upgradability, and other special capabilities into the overall engineering effort.

Figure C-1 shows an important relationship between three parallel aspects of system development: the functional decomposition of a system shown in the center, supportability and logistics shown on the right, and cost shown on the left. As one follows each process flow, activities across each type of requirement are interdependent upon, and impact, one another. This figure demonstrates the importance of trade-off analysis in developing system requirements to balance performance, cost, and other specialties throughout the system life cycle.

SE goes well beyond traditional engineering concepts and tools. In the broadest sense, it encompasses systems thinking and other related systems disciplines



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