In an ordinary Client/Server setup persistent classes are present on both client and server side. However this condition is not mandatory and a server side can work without persistent classes deployed utilizing db4o GenericReflector functionality.
How it works?
When classes are unknown GenericReflector creates generic objects, which hold simulated "field values" in an array of objects. This is done automatically by db4o engine and does not require any additional settings from your side: you can save, retrieve and modify objects just as usual. An example of this functionality is db4o Object Manager.
Unfortunately in a server without persistent classes mode there are still some limitations:
The following topics provide examples of a server without persistent classes usage. We will use a server from the ClientServer example, a separate project for a client and deploy persistent classes only on the client side. In .NET you will need to test the examples on separate machines as the assembly information is loaded in CLR and shared.