Re: RDF-star use cases from Amazon Neptune

Ora,

thanks for these use-cases? Do you want to add an agenda item in today's 
call for discussing them?

Below are my 2¢ about this.

 > RDF semantics (...) stipulate that a triple <s, p, o> is unique 
(...). In LPGs, however, no such restriction exists for edges.

I think that presenting this feature of RDF as a "restriction" is 
unfair, and misses the point. In my view, the impedance mismatch between 
RDF and PGs is not due to some arbitrary restriction on the RDF model. 
It is due to the fact that RDF is a logic, that can be represented as a 
graph, while PG is a graph data model, without any semantic commitment.

An RDF triple (s p o) is a /statement/ before being an edge in a graph. 
It states that the relation (denoted by) p holds between (the things 
denoted by) s and o. That statement is either true or false; therefore 
the triple is either in the RDF graph or it is not.

Either Bob is married to Alice or not. Either there is a pipe between M1 
and M2 or there is none. If finer grained information is required (which 
marriage? which pipe?), then additional nodes must be added (as 
suggested by Jos in his answer, or in 
https://w3c.github.io/rdf-star/cg-spec/2021-07-01.html#occurrences). 
That is a feature of RDF, not a bug.

> [ about the example with  "double-nested" triples ]
 > This is of course a perfectly valid approach, but it does not match 
the typical approach when using LPGs.
 > Note also that, while the example above captures the correct 
semantics, it is awkward (...

It might be awkward, but if it captures the correct semantics, then 
maybe that's the way it should be represented in RDF ;-)

More generally, I strongly believe that, because of the different 
focuses of RDF vs. PG, we should not strive for a one-size-fit-all 
mapping between the two. Different patterns in PGs convey different 
semantics, therefore they should be mapped differently to RDF. This is 
the line of work explored by Julian Bruyat in his PHD (which he also 
presented at the SCG workshop [1]).

   best

[1] Bruyat et al.  "PREC: Semantic Translation of Property Graphs". 1st 
Workshop on Squaring the Circle
on Graphs (SCG2021), SEMANTiCS 2021. 
https://mosaicrown.github.io/scg2021/#mu-schedule



On 02/12/2021 19:43, Lassila, Ora wrote:
>
> Folks,
>
> Attached is a document that outlines a couple of uses cases (variants 
> of one modeling pattern ,really) we would like to submit for 
> consideration by the upcoming RDF-star Working Group. I am submitting 
> these now just in case this turns out to be relevant to how the 
> charter gets written. Comments are welcome, and I am happy to discuss 
> these use cases whenever.
>
> Regards,
>
> Ora
>
> -- 
>
> Dr. Ora Lassila
>
> Principal Graph Technologist, Amazon Neptune
>
> Amazon Web Services
>
> ora@amazon.com
>