RDF Reification

Hi all,

I am trying to write a journal/undo mechanism for RDF statements.

Considering the following arc:

urn:abc => #dc:Title => "bob"

Now if I change the arc's object from "bob" to "fred", I need to store 
the old value to be able to undo later.

(Axel, perhaps you could correct me here) it doesn't seem possible to 
identify a specific arc without the entire triple?

So I can't say the arc ID of "123456" last object was "bob", so first I 
assert:

urn:abc => #dc:title => "fred"

Then to avoid arcs colliding, in a different datasource I assert:

urn:undo:1 => #undo => urn:abc
urn:abc => #dc:title => "bob"

All is well and good until the arc is changed again - say from "fred" to 
"mike"

First:
urn:abc => #dc:title => "mike"

Then the journal assertion:

urn:undo:2 => #undo => urn:abc
urn:abc => #dc:title => "fred"

But I already have an arc for "bob" so now I have no way of knowing 
which arc belongs to which "undo" assertion.

Is this the kind of thing the RDF Reification Vocabulary could be used for?

Something like:

urn:undo:1 => rdf:subject => urn:abc
urn:undo:1 => rdf:predicate => dc:Title
urn:undo:1 => rdf:object => "bob"

urn:undo:2 => rdf:subject => urn:abc
urn:undo:2 => rdf:predicate => dc:Title
urn:undo:2 => rdf:object => "fred"

Not sure if this would be a correct way to use this vocab?


In a similar vein, I'm intrigued when using the mozStorage interfaces 
for RDF as discussed here: 
http://wiki.mozilla.org/Mozilla2:Unified_Storage#RDF_Data_Store_interface
How a triple in a datasource is going to be mapped to a "triple_id" in 
the SQL when saving an assertion? Or is the intention to just use 
nsIRDFXMLSerializer against an entire datasource rather than individual 
arcs?

Cheers,

N