Deciding what to use as the fourth element of the quad

I am assuming (or rather hoping) that some future version of RDF will provide us with the mechanism to store and communicate context information.  By "context" I mean a set of triples which can be named and\or described.  For example, the set of triples that I name ContextA is TruthTheoretic, nonmonotonic and was authored by Jon.  Now this can be implemented 2 different ways that I know of, both of which involves adding an extra element to our beloved triple.   One way involves calling the fourth element the URIref of the context, and the other calling the fourth element the statement id.   I have compared these two different methods in the following mentograph:

http://robustai.net/mentography/quads2ways.gif

We can also use context to express reification by saying that a reified statement is a context containing just one statement.  What is interesting is that the data stored for context-reified statements is the same for both methods discussed.  I have shown this in the following mentograph:

http://robustai.net/mentography/quads2waysR.gif

Personally I prefer the fourth element to be a context URI ... primarily because that seems to be the way it is done in CWM.   It also means that we don't need to grapple with a way to assign URIs to statements, but rather can assign URIs to contexts ... which me thinks is more useful if we intend to share them.   

What do you all think ?

What is also interesting is that the graphic model, the mentograph, is the same regardless of what we decide.  This makes me think that mentography is barking up the right tree.

Seth Russell
http://robustai.net/mentography/