The current description somehow makes sense for JSON-LD, but it isn't very clear as content type independent definition.
Providing a shape in ShEx and SHACL should provide an unambiguous and validatable way of defining it.

I can write one in ShEx, it can also constrain that it has to use IRI and can't be a blank node, it would go something like this:

:Notification IRI {
  a [ as:Update as:Add as:Delete as:Create ] ;
  as:object IRI;
  as:published xsd:dateTime ;
  notify:state xsd:string
}