Re: Consolidating triple/edges -- occurrence set version

Hi Andy,

> On 10. Jan 2024, at 23:46, Andy Seaborne <andy@apache.org> wrote:
> 
> This is a variation of the consolidated triple/edges proposal.
> 
> An issue with the "named occurrences" variation of the consolidate proposal is that given a name part of a named occurrence, there is no way to find out what the subject/predicate/object of the occurrence.

I don’t get this. If 

    << :s :p :o >>         # an RDF-star CG-report triple term

is a triple term as defined in the CG report, and rdfx:occurrenceOf is a relation between such a term and the name of its occurrence in the data (as a regular RDF triple - referentially transparent, naturally)

    :s :p :o .             # an RDF triple

then 

    :X rdfx:occurrenceOf << :s :p :o >> .

describes an occurrence of that triple term as an actual triple [0]. 

SPARQL-star allows to query for the properties of :X, namely for the subject, predicate and object of the triple it describes. So why do you say that "there is no way to find out what the subject/predicate/object of the occurrence" is?



Best,
Thomas



[0] There is a problem with the indirection inherent to this approach: we don’t know if the occrrences describes a triple that actually is asserted in the data. Even if the triple referred to via the triple term actually occurs in the data, it just represents the type. The occurrence described by :X might yet (intend to) refer to an unasserted occurrence. The Nested Named Graph approach avoids that problem.


> There have been suggestions of having virtual property rdf:occurrenceOf (it can not appear in data) or adding an edge set into the RDF data model (a graph is no longer just  a set of triples).
> 
> In this variation, the RDF abstract data model has "occurrences sets" as RDF terms.
> 
> An "occurrence set" for S,P,O is the set of all named occurrences that have S,P,O in those positions. There is one occurrence set for every triple.
> 
> A named occurrences is a pair of (name, occurrence) where "occurrence" is member of an occurrence set.
> 
> Occurrence sets replace triple terms.
> https://lists.w3.org/Archives/Public/public-rdf-star-wg/2023Dec/0033.html
> 
> Named occurrences are not part of the RDF data model (abstract syntax).
> 
> The syntax <<[ ]>> is used below for now to be different to triple term <<( )>>. Had that not been used already, it would be better as <<( )>> because () is often used for tuples.
> 
> An implementation that wishes have great named occurrence performance can have data structure for (n,s,p,o) with indexed lookup operations.
> 
> ## Turtle and N-Triples.
> 
>    << _:n | s p o >> :q :z .
> 
> is a syntax form and is equivalent to the N-triples:
> 
>    _:n rdf:occurrenceOf <<[ :s :p :o ]>> .
>    _:n :q :z .
> 
> "memberOf" or variants on "member" don't look good because rdfs:member already exists.
> 
> Now given a name "n" (blank node or URI) found by some means, then
> 
>    _:n rdf:occurrenceOf ?X .
> 
> finds the occurrence set term, which has the subject/predicate and object.
> 
> Annotation syntax applies as before.
> 
> An RDF graph is a set of triples.
> There is no need for a virtual property.
> 
> It may work to have a class of occurrences for S/P/O where the occurrence set is the class extension.
> 
>    Andy
> 
>

Received on Thursday, 11 January 2024 11:02:27 UTC