Item Definition
Section 11: Aircraft & Avionics Architecture
Definition
The specification of a hardware or software item that results from the functional allocation and system architecture definition process. Item definition establishes the item's functional requirements, performance requirements, interface requirements, environmental requirements, and design assurance level, forming the starting point for the item-level development process under DO-254 (hardware) or DO-178C (software).
Where This Shows Up
Item definition bridges the gap between system-level development (ARP 4754A) and item-level development (DO-254/DO-178C). A well-defined item has clear boundaries, unambiguous requirements, and a specified DAL derived from the system safety assessment. Incomplete or ambiguous item definitions are a common source of problems in avionics development, leading to requirement gaps, interface mismatches, and late-stage certification issues. The item definition typically includes the hardware/software interface definition, which specifies how the hardware and software within the item interact.
Primary Sources
Section 5.3 — addresses item definition as the transition from system-level development to item-level development.
Section 4 — references item definition as the input to the hardware design assurance process.
Section 4 — references item definition as the input to the software development process.
Related Terms
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