Re: Consolidating triple/edges

On Tue, 2023-12-19 at 16:39 -0800, Gregg Kellogg wrote:
> > On Dec 18, 2023, at 12:47 PM, Andy Seaborne <andy@apache.org>
> > wrote:
> > 
> > [...]
> > 
> > So we have:
> > 
> > Occurrence:
> >   << :s :p :o >>
> >   <<| N | :s :p :o >>
> > 
> > Triple term:
> >  <<( :s :p :o )>>
> 
> To be clear, a Triple term would be a type, while an occurrence is a
> token?

That's my reading as well. However, maybe someone with a more intimate
understanding of the subtleties* of the notions of a token and an
occurrence should look at this question.

*https://plato.stanford.edu/entries/types-tokens/#Occ


> Are these fundamental in the abstract syntax? Or is the token
> considered syntactic sugar for something like [] rdfx:occurrenceOf
> <<( :s :p :o >>?

When I read Andy's email, I was assuming the latter, and that's also
what my immediate reaction would be, now that you ask this question
explicitly.

The options that I can currently think of to make tokens/occurrences an
explicit concept in the abstract syntax, would mean that we have to add
another new type of term or introduce some additional mathematical
structure that the notion of an RDF graph would have to be accompanied
with. I don't think these are very attractive options. Yet, if it
appears that there is a use for treating tokens/occurrences in a
special way in SPARQL (e.g., dedicated operators or build-in
functions), then we may have to capture them explicitly in some way
(but I don't see a need for that at the moment).

> Can a term contain an occurrence, or visa-versa? E.g. <<( << :s :p :o
> >> :o1 :o2 )>> or << <<( :s :p :o )>> :o1 :o2 >>?

The latter is probably not particularly controversial, in particular if
we understand expressions of the form

  << :s :p :o >>

as syntactic sugar as suggested in Andy's email. Then, the shorthand

  << <<( :s :p :o )>> :o1 :o2 >>

expands to

  [] rdfx:occurrenceOf <<( <<( :s :p :o )>> :o1 :o2 )>> .

(plus, the blank node in the subject of this triple would then also be
in the subject / the object of the triple in which the shorthand is
used).

Regarding the former, i.e.,

  <<( << :s :p :o >> :o1 :o2 )>>

perhaps this can also be considered (and, thus, defined) as a shorthand
notation for

  <<( _:b :o1 :o2 )>>

together with the addition of

  _:b rdfx:occurrenceOf <<( :s :p :o )>> .

into the same graph in which the shorthand is used as subject or object
of a triple. (Note that _:b is meant to be a fresh blank node
identifier that is not yet used in the document in which these things
are written).

> Would N-Triples contain both variations, or just the triple term?

I can see how supporting both variations in N-Triples maybe appreciated
for some use cases, but it may also be confusing because it would
diverge from the current principle that every line in an N-Triples file
is a serialization of a single triple only. 

(Note that my assumption here is, again, that an expression of the form

  << :s :p :o >>

is really just syntactic sugar.)

> And, to James’s point, can you say << :s :p :o >> a <<( :s1 :p1 :o1
> )>>; if so, would this be the same as rdfx:occurrenceOf?

Well, by resolving the syntactic sugar as suggested in Andy's email,
this would expand to

  _:b rdfx:occurrenceOf <<( :s :p :o )>> .
  _:b rdf:type <<( :s1 :p1 :o1 )>> .

where, again, _:b is a fresh blank node identifier. So, the predicate
"a" (or, rdf:type) in James' triple is not necessarily the same as rdfx
:occurrenceOf.

> > Annotation:
> >  :s :p :o {| :p :z |}
> >  :s :p :o {| N | :p :z |}
> > (the last one is fiddly in the grammar because simply writing in
> > ABNF is ambiguous for some parsers)
> 
> Presumably, an annotation is on an occurrence and not on a triple
> term/type?

I assume that's what Andy is suggesting here.

Best,
Olaf


> 
> Gregg
> >  
> >   Andy
> > 
> 
>

Received on Wednesday, 20 December 2023 09:26:46 UTC