The architecture presented here, at least at the moment, is not meant to be a blueprint for the implementation of the solution, but rather a tool to help me - and others - to understand the problems the project attempts to solve and the constraints within which the solution has to operate.
To capture the architecture I use the C4 modelling notation and UML.
The SDK is outside of the ODIS Service. It is intended to be used by service developers to help with the rapid development of endpoint implementing the agreed search protocol.