I’ve actually been thinking about this the last couple of days. For example, an inventory app for even a small hardware company with multiple suppliers can be overwhelmingly large if you are hosting all their data for your own resupply use.
The way I’ve envisioned it would actually be made much more simple with SQL databases because you wouldn’t necessarily work with the entire database, but you could work with the result set of a complex query. The result set would be the “database” for the app, with all the requisite ID’s for updating the main database through API calls (when necessary).
