Can you elaborate on "federation of databases"? What is your real business requirement? Sounds like you are trying to take advantage of two complete different pega instances (7.2.1 versus 7.1.6 running on different db platforms).
You are correct in that is what we are trying to accomplish. Our management team had attended PegaWorld and talked to people and they had mentioned the term "federated databases" to them and this got the management teams attention.
Here is our scenario, we just upgraded from Pega 5.4 to 7.1.6 after just over a year of work. Most of our code still has references to the 5.4 code. Phase II of our upgrade, once we were stable in production, was to convert ALL of the applications to using out of the box 7.1.6 code and no longer reference any of the 5.4 code.
We found out that we could not update past 7.1.8 because we still had the references to 5.4 code, according to some people at Pega our management team talked with. So they have decided that we need to do a new instance of Pega (7.2.1) and maybe place it in a Windows environment running on SQL server and split schema as some cost saving measures.
It seems that the people at PegaWorld told them that we could do this using the federated database.
Since I am one of the admins of the system, it is up to me and a few other tema members to see (1) if this is possible (2) will it work the way management thinks it will work (3) will it be cost-saving like management thinks (4) and how to accomplish this.
Thanks for the details. The only product coming to mind that multiple pega instances can work together is called federated case management (https://pdn.pega.com/products/federated-case-management), but I am not sure it is what your management talked about. Maybe you can give us the pega contact (names) your management had at PegaWorld, we can then follow up here at Pega to understand more about the background. That way, we can give a much clearer guidance.