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Answer · from the public record
What is a cluster of PII under ISO 27555?
A cluster of PII is personally identifiable information processed for one consistent functional purpose. It is defined independently of how the data is stored, and it can include paper. One record can sit in several clusters, and each cluster is allocated one deletion rule.
Last updated: 2026-10-22. Evidence level: public record and public sample. The licensed text is not reproduced.
The definition
Clause 3.1 defines a cluster of PII as information processed for a consistent functional purpose, and the note says clusters are described independently of the technical representation of data objects. The practical effect is that a cluster is a purpose container, not a system container.
Why purpose and not system
A customer record can sit in a CRM, a billing platform, a support tool and a mailbox. Four systems, one purpose, one deletion decision. A register built from the system inventory gives four rules and no owner. A register built from purpose gives one row with four systems, one owner and one rule.
One record, several clusters
The draft allows the same information to appear in more than one cluster. An invoice can be bookkeeping data, part of an engine history file and part of a supplier file, each with its own period and starting point. The register must show the copies rather than pretending there is one.
What the register should hold
A purpose, a functional owner, the data objects, the systems, the formats including paper, the deletion rule and the deletion class. The owner has to be a business role, not a system administrator, because the owner decides the purpose and the exceptions.
What it is not
It is not a table, a folder or a retention label. It is not a legal category, although law can shape the period. And it is not fixed forever: a change of purpose can move a data object to another cluster, which is the subject of clause 7.4.3 in the DIS.
Check the source. The full record, the stage trail and the clause pages are free. Start with the clause 6 page.