There's a as of yet undefined concept of references (like Clojure's references) and data flow analysis so that we can determine if a call is made from the "scope of a reference".
References and reference scopes represent external resources that cannot be easily represented by sources and sinks.
Data persistance is one of the reference/scope pieces. I'm figuring that I'll use MongoDB or something like it because Mongo's BSON data representation dovetails with Visi's guarantee that all user-generated data structures can be BSON serialized.
I'm currently working on a scope for Objective C so that I can get Visi to be self-hosted (basically, Visi will be able to call and subclass ObjC objects).
Once I get that scope working (which will mean I'll have a provisional syntax for references and scopes), I'll work on a persistance reference.
Hope this helps.