Types and Occurrences - was: Re: "Multi-Edge Support in RDFn" slides

Pierre-Antoine,

> On 14. Dec 2022, at 23:23, Thomas Lörtsch <tl@rat.io> wrote:

>> On 14. Dec 2022, at 21:20, Pierre-Antoine Champin <pierre-antoine@w3.org> wrote:

>> On 13/12/2022 14:25, Thomas Lörtsch wrote:

>>> Doesn’t that overcome RDF-star's syntactic safe guard against paradoxes? And if it does - I’m not a logician, so I’m not sure - aren’t the consequences even worse for RDF-star than for RDFn, as the paradox targets all occurrences of type << :A a :Lie >>, not only one instance as in RDFn’s case.
>> Not, it does not targets all occurrences, because the occurrences are distinct from the type -- or, as you phrase it in terms of the type-token distinction: the tokens are distinct from the types. That's why it's called type-token distinction. :-)


to put it more succinctly: 

 even a type occurs, and can do so many times. 

When I annotate << a b c >> then I annotate << a b c >> in all the places it does and may ever occur. When I annotate a statement identified by an ID in RDFn (or RDF/XML, for that matter) then I annotate only one statement occurrence. 

It is in the end a question of perspective and of use case if one puts the emphasis on
- what distinguishes those statements as occurrences or
- what they have in common - their type. 
The source of a triple may be administrative detail first, not a distinguishing feature, emphasizing the type interpretation, but it may become an important aspect later, emphasizing the occurrence aspect, or vice versa. The syntax should get out of the way and not require the modeller to make such decisions. Hard coding them into different modelling primitives makes the data less useful in the long run.

Another issue is that of multipart annotations, but the two issues result in the same problem when modelling: they require intermediary nodes. If those nodes need to be created explicitly, they change the triple topology in modelling and querying. Both problems are easier and more sustainable to solve when each triple is provided with an occurrence identifier right away and using that identifier is mandatory for any kind of annotation.


Best,
Thomas


> The quoted triple << :A a :Lie >> is by the CG report defined to be a type that means the same everywhere. So everything that is asserted about it is asserted about that type everywhere it is used as term in an assertion (to avoid saying "everywhere it occurs").
> 
> An occurrence OTOH, as described by RDFn or RDF standard reification or by :X in 
>   << :A a :Lie >> :hasOccurrence :X
> occurs only once. So the paradox would be more "contained". If that makes much of a difference in practice is another question. It seems a little more harmless to me, but a reasoner might be just as upset either way.
> 
> 
> Thomas
> 
> 
>>  pa
>>> I haven’t fully understood how the RDF 1.x semantics tackles this topic [0] but as I said before my intuition is that going the way of occurrences (which in my understanding is a more generic term for both instances and subtypes, which - see OWL punning - are rather application specific categories) opens the same venue: interpreting a statement as a concrete occurrence of the type instead of as the type itself (as the RDF-star semantics proposes) separates the two, puts the occurrence in the extension of the type, and thereby avoids paradoxes in the semantics already.
>>> 
>>> Thomas
>>> 
>>> 
>>> [0] 
>>> https://www.w3.org/TR/rdf-mt/#technote
>>> 
>>> 
>>> 
>>> 
>>>> On 9. Dec 2022, at 08:15, Pierre-Antoine Champin <pierre-antoine@w3.org>
>>>> wrote:
>>>> 
>>>> Thanks Souri,
>>>> 
>>>> I added a link to the slides in the minutes of the call where you presented them.
>>>> 
>>>> https://www.w3.org/2022/11/17-rdf-star-minutes.html
>>>> 
>>>> 
>>>> A few remarks about slides 8 and 9: 
>>>> - what you call semantics in these slides is more related to the RDF abtract syntax [1] than the RDF semantics [2]. The former is about structural elements of RDF (IRIs, triples...) while the second is about the "things in the world" that the RDF graph is about.
>>>> 
>>>> - In those slides, I see no constraint about preventing triples to talk about themselves (which the CG report explicitly forbids [3]). This allows for something like
>>>> 
>>>>  :t1 a :Lie (:t1).
>>>> 
>>>> or, even more tricky to detect
>>>> 
>>>>  :t2 a :Truth (:t1).
>>>>  :t1 a :Lie (:t2).
>>>> 
>>>> This kind of paradoxes may be tricky to model in terms of semantics....
>>>> 
>>>>  pa
>>>> 
>>>> [1] 
>>>> https://www.w3.org/TR/rdf11-concepts/
>>>> 
>>>> [2] 
>>>> https://www.w3.org/TR/rdf11-mt/
>>>> 
>>>> [3] 
>>>> https://www.w3.org/2021/12/rdf-star.html#concepts
>>>>  "Note also that, by definition, an RDF-star triple cannot contain itself"
>>>> 
>>>> On 03/12/2022 00:21, Souripriya Das wrote:
>>>> 
>>>>> Attached a revised version of the RDFn slide deck [1] that includes
>>>>>  • (slide 8) new slide titled "RDFn Semantics: Essentials, in a few words"
>>>>>  • (slide 9) corrected slide titled "RDFn Semantics: Essentials Beyond RDF" that now states that TI INTERSECT TE need not be an empty set and shows the corrected diagram
>>>>>  • (slide 14) new slide titled "Enabling Explicit Naming in RDF-star, Serializations, and SPARQL-star" 
>>>>> Thanks,
>>>>> Souri.
>>>>> 
>>>>> [1] 
>>>>> https://lists.w3.org/Archives/Public/public-rdf-star-wg/2022Nov/att-0016/RDFn_WG_Slides.pdf
>>>> <OpenPGP_0x9D1EDAEEEF98D438.asc>
>>>> 
>> <OpenPGP_0x9D1EDAEEEF98D438.asc>

Received on Thursday, 15 December 2022 16:01:36 UTC