we need to specify how an other app could find the right data.
This is very related to [Post deleted] - #7 by mrkvon; that is, in the long term, if we adopt a hybrid-kg model then we decouple data and location. But that doesn’t provide you with a solution that works right now.
Right now your best option with publically available specifications is probably to add this information to a type index when you write to a Pod; so any other apps that use type indexes can find the location of the data that you wrote. If you need help with the spec @Timea might be able to lend a hand.
It’s not just about the choice of ontology, you also need to document which data shapes you expect […] all of those conventions together define what expectations a second app can have when reading data from a pod, that was written there by a first app.
I largely agree with this, and it is one of the reasons why I (personally) see type indexes as useful/necessary in the short-term but not a mid-long term feature of Solid; as they are unable to express these kinds of requirements.