You need some kind of global (or not-so global) persistent namespace. And ability to interoperate with the outside world. It's not a bad idea to have a separate API for managing persistent state vs ephemeral state -- or at least that's not a bad convention we've developed over the years in order to allow for some sanity in state management. Persistent image-based systems like Smalltalk tend in my experience to degrade to a confusing mess and become difficult to reason about over time unless you end up introducing concepts that start looking suspiciously like files.