Tag number

A tag — P-101A, FT-2034 — is an address in the plant's namespace. The tagging convention encodes meaning into its structure: item type, unit or area, sequence, suffixes for parallel items; and once assigned, the tag is how the item is referenced on the P&ID, in the datasheet, on the purchase order, in the maintenance system and on the nameplate bolted to the thing itself. Tags are what make the facility's information joinable: every document that mentions FT-2034 is talking about the same instrument, and the tag is the proof.

Except when it isn't — and that exception is a whole category of industrial pain. Conventions drift between projects and eras; vendors ship items under their own numbering; brownfield sites accumulate retagging campaigns, legacy tags and duplicates; and the same equipment can live under different identifiers in the engineering archive and the maintenance system. Reconciling identity across those variations is, formally, an entity-resolution problem — and it is the unglamorous first task of every data-integration, digitalisation and revamp effort ever attempted on an existing plant.