Hi, would like you guys' advice. Let's say we have system A, system B and system C and each system has its own user management module/tables. Meaning system A's user management module is at database A, system B's user management is at database B and system C's user management is at database C.
Now, we plan to centralized user management module by creating a separate database, say database D and to have system A, B and C to use user management in database D. Once successfully, those user management tables in database A, B and C will be removed.
In this design, do we need some kind of database middleware for system A, B and C to connect to database D. Secondly is what if system B need to add a special field in a user management tables in database D?