What is a User?
In Gem's ecosystem, a User is a collection of objects protected the User's login credentials. The relationships between a User and other objects in Gem, like Connection and Profile, may be maintained outside of Gem. The partner application would be responsible for storing and correlating User, Connection and Profile access tokens generated by Gem. To reiterate, a User may have one or many Connections and Profiles, while a Connection or a Profile may relate to a single User.
Partner applications may also correlate its users to Gem Users and maintain a mapping between the two, rather than maintaining a full mapping between its users and every Gem Profile and Connection. You can choose what model fits your application best.