Single identifier namespace for PROTECT-CHILD record business identifiers (patient, donor, visit, transplant, and all per-visit clinical/lab/medication/specimen/event records). The resource type distinguishes the kind of record. Identifiers follow one convention: TOKEN-CENTRE-SEQUENCE, for example REC-1-0001 (patient, centre 1, sequence 1) or LBR-1-0006 (lab result); study-wide catalogue entries such as lab tests are not centre-qualified and use TOKEN-SEQUENCE, for example LBT-0001. Identifiers carry no clinical meaning.