Caching recommendations / affordances

[NoelDeMartin]

In the discussion at #40, we've talked about caching profiles as a way to reduce network requests in subsequent visits to an app. That, however, introduces the dilemma of when to invalidate the cache.

Given that we're considering giving recommendations on how to handle profiles in apps (for example, saying that apps should fetch all the documents), I wonder if we should also give recommendations on how to cache and invalidate this data.

Furthermore, having into account that it's impossible to really know when something has changed, it may be useful having some triples indicating the last time anything in the profile was updated. That way, apps could cache a profile indefinitely until this value changes and this could be checked with a single request. This is similar to something we've already been discussing in the Solid spec: solid/specification#227 (comment)