- Asset — a serialised physical thing, with a tag, a category, a location, an owner, a status and a criticality.
- Obligation — anything time-boxed: a licence, permit, certification, calibration certificate, warranty or contract. It has an expiry and optionally a cancellation deadline and a renewal lead time. It may belong to one asset, or to the whole organisation.
- Plan — a recurring commitment such as preventive maintenance, calibration, inspection, validation or a condition check.
- Evidence — an event that records what happened: maintenance, repair, calibration, inspection, incident or decommissioning, with its outcome.
Why they are separate
A spreadsheet row holds all four at once, which is why one date column ends up doing the work of three. Separating them lets one asset carry a dozen certificates with different expiries, lets a site permit exist without pretending to be a machine, and lets the history show the calibration that happened rather than overwriting it with the next one.
Around them
- Organisation — the boundary. Nothing crosses it; every query is scoped by it.
- Event log — every change is written to an append-only history in the same transaction as the change itself.