Before the reporting of Customer Account Information and Customer Identifying Information begins with the implementation of Phase 2e (Full CAIS), regulatory users of the CAT will use FDIDs to identify whether the same account is trading within a single broker-dealer. After the reporting of Customer Account Information and Customer Identifying Information begins, FDIDs will be used to link accounts to specific Customers, including mapping accounts with common ownership (for instance, where a Customer is associated with more than one FDID).