Re: Consolidating triple/edges

On 21/12/2023 15:50, Niklas Lindström wrote:
> On Thu, Dec 21, 2023 at 12:42 AM Gregg Kellogg <gregg@greggkellogg.net> wrote:
>>
>> I created a Draft PR [1] with some Turtle Grammar changes based on my interpretation of Andy’s concept. You can see the rendered version of the EBNF via GitHack [2].
>>
>> As I noted, the change to the “annotation” production makes it context-sensitive, as an LL(1) parser would get confused when seeing the IRI/BlankNode that could either identify the triple occurence or be a predicate annotating the annotation, which requires the parser be able to backtrack. Not really a problem for more modern parsers, but a notable divergence. Other alternatives in the grammar could eliminate this at the cost of being less intuitive.
> 
> For naming annotation occurrences, I think it's best to allow either
> predicateObjectList:
> 
>      <s1> <p1> <o1> {| dct:source <x> |} .
> 
> or iri or BlankNode. Not sure how to do that nicely; I've previously
> suggested [1] (some use case examples at [2]):
> 
>      <s1> <p1> <o1> {_:a1} .
>      _:a1 dct:source <x> .

Have an explicit name in annotation syntax is covered by

    :liz :spouse :dick {| id:1 | :start 1964; :end 1974 |} .

(it's ambiguous for a lookahead of one in LL but it seems to me to be 
more consistent in style c.f. << N | :s :p :o >>

Generally, keeping away from single-character { } because of the use in 
SPARQL and possible for a graph-solution is probably a good hope.


> Whatever exact syntax we end up with, that design follows the regular
> "flat" Turtle design of allowing nested descriptions only for
> unlabelled blank nodes (as in blankNodePropertyList), and otherwise an
> identifier (iri or BlankNode) with a regular description of that
> occurrence.
> 
> We might "bikeshed" some more going forward. Noting the old thread on
> this, particularly the actual *star* alternative [3]; not sure if this
> would work, but it could be nice:
> 
>      <s1> <p1> <o1> *_:a1 .
>      _:a1 dct:source <x> .
> 
> Best regards,
> Niklas
> 
> [1]: https://gist.github.com/niklasl/4f52c32ef2d888c172c8584e36c24610#proposal-rdf-star-annotation-occurrences
> [2]: https://gist.github.com/niklasl/2d02902b81e215b1795981df31927e9b
> [3]: https://lists.w3.org/Archives/Public/public-rdf-star/2021Jan/0027.html
> 
> 
>> Gregg Kellogg
>> gregg@greggkellogg.net
>>
>> [1] https://github.com/w3c/rdf-turtle/pull/51
>> [2] https://raw.githack.com/w3c/rdf-turtle/triple-term-occurance/spec/turtle-bnf.html
>>
>> On Dec 20, 2023, at 2:51 AM, Pierre-Antoine Champin <pierre-antoine@w3.org> wrote:
>>
>> Just to concur 100% with Olaf's interpretation of Andy's email.
>>
>> On 20/12/2023 10:26, Olaf Hartig wrote:
>>
>> 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
>>
>>
>> <OpenPGP_0x9D1EDAEEEF98D438.asc>
>>
>>
>

Received on Thursday, 21 December 2023 16:00:01 UTC