RE: statements about a graph (Named Graphs, reification)

>From: "Michael Schneider" <schneid@fzi.de>
[...]
>
>The third candidate is NamedGraphs. But in order to estimate if this
>approach can be used for the above scenario, I need to know more about it.
>This was the reason why I asked in my last mail "How do named graph data 
>get
>published into the Semantic Web?".

GF> I guess the answer is 'the same way as that of RDF'. The paper "Named 
Graphs, Provenance and Trust" by Carroll, Hayes, Bizer and Stickler mention 
RDF/XML as a feasible realization, but with disadvantages: I quote them:
"Using RDF/XML has disadvantages: [...] The URI at which an RDF/XML document 
is published is
used for three different purposes: as a retrieval address, with an 
operational semantics; as a means of identifying the document; and as a 
means of identifying the graph described by the document. There is potential 
for confusion between these three uses."

Can I then just go ahead then and assume that every RDF document defines at 
least one (un)named graph, which is the URI of the document itself?

>If it is (with reasonabe effort) possible
>for instance to search for the URIs of all NamedGraphs of the form
>
>      :g { me:alice foaf:knows he:bob }
>
>then NamedGraphs work equally well like Reification for this purpose,
>because I can then, in a second step, query for all those triples in the
>SemWeb, which have the found NamedGraph's URI as their subject. And
>NamedGraphs would bring this big advantage with them that they can talk
>about more than a single triple (though I have difficulties to see what 
>this
>serves me in my usecase above. Perhaps other people will be able to find an
>example, where searching for annotated "multi-triples" would really make
>sense).
>
>But, we must not conceil that NamedGraphs have a very bad disadvantage in
>comparison with Reification, anyway: NamedGraphs are not a standard. And if
>this approach does not get into RDF, or at least into common use, very 
>soon,
>it will possibly lose its chance to become a player at least in the above
>scenario.

GF> I guess you were on to something (or onto something :) I guess what I 
needed was named graphs with custom reification. I need the grouping feature 
of named graphs, and I need reification for making statements about the 
group. Starting from what's out there, I don't need too much more from named 
graphs: I just need the missing semantics of tying the URI of the document 
to the RDF graph in it. This is the part where RDF is deliberate silent in 
reification, from what I (almost) understood. I would say that the use of 
this custom reification 'scheme' is strong enough to standardize it along 
with Named Graphs themselves. It's actually a better fit for 'making 
statements about statements'.

>
>/This/ will of course only be a topic /if/ the above scenario is relevant 
>at
>all.

GF> I think it is a very relevant scenario.


Kind regards,
Gustavo Frederico

Received on Thursday, 6 September 2007 04:12:59 UTC