U21A9

U21A9 is a fictional alphanumeric identifier used in the illustrative Universal Item Registry (UIR), a hypothetical standard employed in this encyclopedia's example datasets. The code serves as an example of how such identifiers are structured to encode category, subcategory, and variant information within a single string.

Structure and encoding. The designation begins with a single letter, followed by two digits, a capital letter, and one or two digits (in the base form). In the UIR, 'U' signals a unit-type record, '21' indicates the main subcategory, and 'A9' specifies the particular variant. Optional suffixes after a dash denote revisions or status (for example, U21A9-01 may indicate the initial revision).

Data associated with U21A9 includes a name, a brief description, a manufacturer or owner, dates of introduction and retirement, and provenance data such as origin, batch, lot, or version history.

Usage in the registry: U21A9 entries are used in supply chain simulations, asset tracking exercises, and educational demonstrations of registry design, data validation, and query interfaces.

Variants and governance: The registry supports variants such as U21A9A and U21A9B to represent minor revisions. Governance rules specify allowed suffixes, checksum validation, and deprecation policies to avoid code collisions across domains.

In fiction and instructional contexts, U21A9 is frequently paired with related codes such as U21A8 and U21A10 to illustrate cross-referencing and relational queries.