# Internal IDs in the Trial Management data model

In the Trial Management data model, the content of the Internal IDs folder depends on the level of nesting for a report element. The more nested an element is, the more internal IDs are available.

For example, the Internal IDs folder for the Subjects report topic focuses primarily on subject identifiers (primary keys), whereas the Visits Internal IDs folder contains unique identifiers for both visits (primary keys) and subjects (secondary keys).

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