What is person_id, employee_number, user_id in Oracle HRMS?

Person_id is always unique across all the business groups
Employee Number is Unique in the business group, but need not be unique in multiple business groups.
BG-1 can have employee number =1,
also BG-2 can have employee number =1
But there can be only one person_id as person_id =1

Ideally one Employee should have only one username or user_id, but Organizations can take different approach based on the system design or business requirement.
Employee can have multiple usernames when he is transfer from one BG to another.
OR Organization can link the new person_id with OLD user_name to keep Username same.

-- Soham Khot
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