Hi Alan,
On 03/16/2013 01:49 PM, Alan Ruttenberg wrote:
David's assertion that a uri can mean different things in different
graphs is an opinion
An opinion? It is direct consequence of standard RDF Semantics! Read
the spec:
http://www.w3.org/TR/rdf-mt/
The RDF semantics is only defined for a *given* RDF graph. It does not
constrain a URI's resource identity across *different* graphs. And here
is a trivial existence proof that demonstrates that a URI does *not*
necessarily denote the same resource in different graphs.
Graph 1 (assuming standard owl: prefix):
<http://example/h> a <http://example/WhiteHorse> .
<http://example/WhiteHorse>
owl:disjointWith <http://example/BlackHorse> .
Graph 2:
<http://example/h> a <http://example/BlackHorse> .
<http://example/WhiteHorse>
owl:disjointWith <http://example/BlackHorse> .
Each graph (by itself) has satisfying interpretations per standard RDF
(and OWL) semantics. And <http://example/h> denotes a resource in each
graph. But clearly it denotes a *different* resource in each graph.
that does not concur with either the
web specifications
Correct. As I pointed out, the AWWW's statement that "a URI identifies
one resource" is a good goal, but it does not concur with standard RDF
semantics.
nor the goals they were built to satisfy. Caveat emptor.
Not true! As I said before, I *agree* with the goal stated in the AWWW,
that a URI should denote one resource! But that does not change the
reality: that a URI does *not* necessarily denote only one resource.
I also think world peace is a good goal, but it is *not* the reality.
If we're going to make the semantic web work, we need to keep the goals
in mind while *also* recognizing the reality. Facing reality should not
be construed as dismissing the goals. We cannot simply wish the reality
away. We need to do the engineering to make it work.
David
