You are correct: no one is going to rate all their friends across every trust domain that exists. Because there is no upper limit to the number of domains that can exist! Which is why this method doesn’t expect you to rate everybody on everything. A few ratings in a few general categories will be enough to get the system up and running.
My proof of concept demos curation of simple lists. Next on the docket: curation by your grapevine of a graph. In theory, any graph, defined as a set of nodes connected by edges. But importantly: we will use graphs to represent context. Your grapevine will curate graphs of context-categories that will be arranged in a hierarchy. This will allow default influence scores to be inherited down the hierarchy.
Suppose I’m in the mood to watch a drama. Alice recommends you as having good taste in movies, but she didn’t specify dramas specifically. That’s ok; dramas is a subcategory of all movies, so my grapevine pays attention to your recommendation on dramas bc it defaults to your trust score in the more general category of movies, higher up in the tree of categories.
This article discusses in more detail what I mean by context and how influence is inherited.