annotation protocol

I am not clear on what we mean when we talk about protocol with respect to annotations.

In my view of the world of annotations, ProviderX has a database of resources, for example, journal articles. UserA reads an article and creates an annotation.  That annotation is a resource created on some annotation database that userA has access to create an annotation on (obviously, not on ProviderX's database).    UserB (unrelated to UserA) comes across that article and want to see annotations of the article.

How does UserB discover UserA's annotation (or for that matter any annotation of that article)? UserB doesn't even know of the existence of UserA and his/her annotation database.

Is this what we mean (or part of what we mean) by annotation protocol?

Pardon the na?ve question but I don't see this addressed in the model.   It is something I've wondered about for quite a while and don't have an answer.  But I speculate that part of the process is that when UserA creates the annotation,  ProviderX is somehow notified of its creation and can choose to point to that annotation, and then UserB can find it.

Is this issue addressed anywhere in any greater detail than this vague description?  Or is this to be part of the "protocol" to be developed.

Apologies if this has all been addressed and solved,  and I just can't find it.

Ray