Allow to select product systems as provider of a flow in the "Inputs/Outputs" tab of a process

[ghost]

Hello, I have a feature suggestion.

If I am not mistaken, currently product systems can only be set as the provider of a flow in another product system's model graph. It would be very nice if a product system could already be selected as the provider of a flow in the Inputs/Outputs tab of a process.

Just a thought :) Keep up the great work!