I want to know what Orion's Federation feature is.
I have read the Orion documentation and tried the federation function, and the data was registered in all three Orions.
I thought that the second Orion acts as a Proxy and does not store data, but is that not the case? If all three Orions store data, is it correct to say that the Federation does not have its own function, but is a concatenation of Subscriptions?
The Federation mechanism you refer is the one on the documentation. In this case, it is based on subscriptions that copy the data among the brokers on entities changes.
Orion also has the registration and request forwarding mechanism. This case, once the register is done, the Context Broker forward the requests to the one registered. This approach sounds closer to the one you are describing but I encourage you to use the first method (based on subscriptions) since all the advanced operations like filtering are working without issues.
A well-designed Federation should not allow value shadowing by a local database. Unfortunately, that's not a feature offered by design by the Orion Broker. That is up to your design and nothing prevents the shadowing, as far as I understand i.e. even you have registered a provider for an Entity, someone can create locally such an Entity, which may be a mess and a source of conflict.
An alternative that may work is to perform the Federation by a REST Service custom built by you that just acts as a proxy against different Orion Brokers. If this custom service is a single entry point you could guarantee a pure Federated system with no shadowing of values.
