Question

I like the idea of having Interfaces and Implementation separate. But how separate? Are the Interface definitions in a separate .Net assembly? Do you have a single project that defines all Interfaces for a solution? Otherwise are there issues with circular dependencies of Interfaces?

Answer 1

Put your domain objects and interfaces in a seperate ‘domain’ assembly.
This assembly should never reference anything but the core .net assemblies.

This way you get a clean seperation from your domain/service model and your implementation.

Edit:
http://jeffreypalermo.com/blog/the-onion-architecture-part-1/