III.E.8.Set-Relationships [Mandatory, if other set members exist]
Identifies the record as belonging, for business purposes, to an overall set of records. Can consist of the classification of that set, or the Record-Identifier(s) of other records.

III.E.9.Dynamic-Relationships [Mandatory, if higher/lower exists]
Identifies what data is required from other records/files in order to populate other values. This is active in set relationships where a record cannot be opened unless the contents of other records are available.

IV.A.6. Linked-Prior Transaction [Mandatory, if applicable]
Identifies the Record-Identifier(s) for transactions that are part of the same business activity.

IV.A.7. Action-Requested [Optional, good practice]
Identifies if an action was requested as a result of the transaction. Could enable links to past transactions if they occurred.