Active User ID link between HCM and ERP

[nagaret01]

I need to generated all active User ID in ERP for licencing purpose.

This is the situation I have is
1. HCM and ERP system are two different clients
2. HCM : HR key user maintains all the new employee and resigned. the records on employee is clean.
3. ERP not all employees get User ID. Some employee gets User ID months after joining the company.

I pulled out active User ID in ERP. I randomly took one User ID from ERP but noticed that this User ID employee has resigned (inactive) in HCM.

Question
1. How do i pull active User ID in ERP which are still active employee in HCM?
2. What is the primary key between ERP and HCM system?
3. How would HCM know which employee has SAP ERP User ID? Does Basis have to inform HR Key User the moment he creates User ID, so that HR key User can maintain in HCM?

[vishvanadh]

Infotype 0105 stores the information on user id. You can access the data using SE16 - P0105 table.