see also: notes about these diagrams
A URI identifies a resource, which has a representation.
This is something of an idealization. We present a refinement below, where consider each Resource to be a mapping from protocol messages to actual referents. Protocol messages act like interpretations (or perhaps possible worlds) in this way.
The resource is represented in multiple data formats; i.e. multiple Internt Media Types.
Each Internet Media Type tells how to evaluate a fragment identifier as an expression with respect to the data of a representation in that media type. For example, the HTML specification says how to evaluate a fragment identifier given an HTML document.
URI references facilitate exporting a self-referential group of resources from a smaller context to a larger context.
Representations are communicated between agents via messages in communication protocols, e.g. HTTP.
Messages provide context in which to interpret URIs.
This RDF ontology connects my earlier work formalizing HTTP caching in larch and various bits of research into logic and protocols (e.g. Guha's thesis on contexts) with recent www-tag sw-meaning discussions of the meaning of URIs as referring expressions in data formats and formal systems: