Re: Presentation about reifiers and graphs

> On 17. Sep 2024, at 06:21, Franconi Enrico <franconi@inf.unibz.it> wrote:
> 
> On 17 Sep 2024, at 05:20, Thomas Lörtsch <tl@rat.io> wrote:
>>> Slides 19 and 20 ==> Uh? It is not clear at all what you want to say. It i probably enough to say: a set of triples associated to the same identifier can not be seen as a named graph, since the scope of the bnodes in that graph is not limited within that graph but it spans the whole main graph.
>> 
>> Not necessarily, as "Blank nodes can be shared between graphs in an RDF dataset." [0]
>> [0] https://www.w3.org/TR/rdf11-concepts/#section-dataset
> 
> In the above “encoding” of a named graph, blank nodes MUST be shared between graphs in an RDF dataset.
> Datasets have two formalisations of semantics [1]: default graph as union or as merge, characterising exactly the sharing or not sharing of bnodes.
> In Trig, a blank node label represents the same blank node throughout the TriG unique document, i.e., blank nodes sharing the same label in differently labeled graph statements are considered to be the same blank node.
> In general, when named graphs in a dataset have different origin, you cannot assume that the same blank node label in different named graphs represents the same blank node.
> 
> My conclusion: these things need to be discussed, and we haven’t done it yet, and therefore I’d restrain to say that we can represent named graphs.

Nice summary, and I agree with this conclusion! It is slightly different from your comment above which was more sounding like "it is NOT possible" (and that triggered my reply).
 
We should discuss this topic a bit more before we decide how to formalize well-formedness conditions of triple term reification. It would be a shame if we made it inadvertendly impossible to represent named graphs with triple terms. This discussion makes me even more leaning towards an approach that defines some properties (rdf:reifies, and hopefully also rdfs:states) with precise semantics, but doesn’t rule out anything else (except triple terms in subject position! ;-)

.t



> —e.
> 
> [1] https://www.w3.org/TR/2014/NOTE-rdf11-datasets-20140225/#default-graph-as-union-or-as-merge
> 
>