I look at it as EC and S. It's a datastore keyed by Entity handles that lets look up Components. Data transformation is then driven by Systems. The behavior of a game is then driven by the tick order of the Systems.

From this view of the world it's fairly obvious that other structures need to reference entities through their handle. Or in the case of middleware with its own view of the world a translation layer keeps things synchronized.

Stay tuned then. I was already planning to write something about scene graphs and component-based models. Nothing forbids to write also about the rest.