Contract First approach for OPC UA server in SwaggerHUB

Hello All

I am looking for a approach to describe an OPC UA server in a contract. I have a local OPC UA server. The endpoint url starts with opc.tcp(...). After that, I want to describe in the same contract, how a PLC, which is a OPC UA client, take a function and give a answer back.

I have found something in SwaggerHUB, where user have build an API for a access to an OPC UA server or for a OPC UA module. But I did not understand the meaning of it, how it works there. 

Can anyone help me?

Thank you