Re: Making querying of annotations optional



> On 15 Aug 2024, at 17:25, Thomas Lörtsch <tl@rat.io> wrote:
> 
> 
> 
> Am 15. August 2024 16:45:29 MESZ schrieb Franconi Enrico <franconi@inf.unibz.it>:
>> Before letting this discussion go too far, I want to be sure that we share the same assumptions.
>> [0] assumes a CG-style notion of triple reification, which is not the one adopted by the current baseline.
> 
> I don't think so: IIUC embedded triples in [0] are asserted and referentially transparent types, wheras in the CG report they are unasserted and referentially opaque types.

[0] does not define a semantics for RDF*, nor simple entailment, but syntactically [0] has an abstract syntax mirroring the CG syntax, where there is no distinction between triple terms and triple reifiers; and SPARQL* in [0] is not based on BGP matching.
I’ve nothing against [0], I am only observing that is quite far away from our baseline.
—e.


> 
> . t
> 
>> The current baseline has a clear definition for simple entailment, which  remains the basis for BGP matching in SPARQL.
>> --e.
>> 
>>>> On 15 Aug 2024, at 14:10, Thomas Lörtsch <tl@rat.io> wrote:
>>> 
>>> Hi Olaf,
>>> 
>>> 
>>> thank you very much for the correction, and the detailed response!
>>> 
>>>> On 15. Aug 2024, at 10:41, Olaf Hartig <olaf.hartig@liu.se> wrote:
>>>> 
>>>> Hi Thomas,
>>>> 
>>>> I just want to respond to your analysis of querying in RDF* (i.e., my
>>>> earlier work prior to the RDF-star CG), because your claims about it
>>>> are wrong.
>>>> 
>>>>> On Thu, 2024-08-08 at 18:02 +0200, Thomas Lörtsch wrote:
>>>>> [...]
>>>>> 
>>>>> QUERYING IN RDF*
>>>>> ================
>>>>> 
>>>>> In a paper on RDF* and SPARQL* [0] the following example data is
>>>>> given:
>>>>> 
>>>>> :bob foaf:name "Bob" .
>>>>> <<:bob foaf:age 23>> dct:creator <http://example.com/crawlers#c1> ;
>>>>>                    dct:source <http://example.net/listing.html> .
>>>>> 
>>>>> Note that this is RDF*, not RDF-star, and the statement ':bob
>>>>> foaf:age 23' is considered to be true in the graph, i.e. stated.
>>>>> 
>>>>> Then the following query is presented:
>>>>> 
>>>>> SELECT ?x ?age ?src
>>>>> WHERE  { <<?x foaf:age ?age>> dct:source ?src . }
>>>>> 
>>>>> Since the ?src is explicitly asked for, the query seems sensible. But
>>>>> what if one doesn’t care for the source? What if one doesn’t care if
>>>>> a source annotation is provided at all? What if one isn’t even aware
>>>>> of the possibility that an annotation might have be added? It seems
>>>>> that a query for people's age that isn’t aware of that peculiarity
>>>>> will not return Bob’s age.
>>>>> IIUC
>>> 
>>> 
>>> I’m glad I added that caveat ;-) Obviously I’m challenged reading abstract definitions.
>>> 
>>>>> the following query
>>>>> 
>>>>> SELECT ?x ?age
>>>>> WHERE  { ?x foaf:age ?age . }
>>>>> 
>>>>> will not return any results, although Bob’s age is considered to be
>>>>> "in the graph".
>>>> 
>>>> Wrong! By the evaluation semantics for SPARQL* as defined in the paper
>>>> (see Definition 3 in [0]), the result of this query over the example
>>>> data above consists of the solution mapping
>>>> 
>>>>  m = { ?x -> :bob, ?age -> 23 }.
>>>> 
>>>> Notice that the formula in Definition 3 says η[B] ⊆ T+(G*), where
>>>> T+(G*) denotes the set of all RDF* triples
>>> 
>>> 
>>> I had to look that up again, in particular sentence 1 which says that any standard triple is also an RDF* triple:
>>> 
>>> Definition 1.
>>> An RDF⋆ triple is a 3-tuple that is defined recursively as follows:
>>> 1. Any RDF triple t∈(I∪B)×I×(I∪B∪L) is an RDF⋆ triple; and
>>> 2. Given RDF⋆ triples t and t′, and RDF terms s ∈ (I∪B), p ∈ I and o ∈ (I∪B∪L),
>>> then the tuples (t, p, o), (s, p, t) and (t, p, t′ ) are RDF⋆ triples.
>>> 
>>>> in RDF* graph G*, including
>>>> those that are (recursively) embedded in other RDF* triples of G* (as
>>>> defined in Section 2.1 of the paper).
>>> 
>>> This does indeed make much more sense to me than what I wrongly understood the definition to be (and argued about above). It seems like this is very similar to how I would like the proposed 'rdfs:states' to be defined. I hope I’m not again overlooking something important.
>>> 
>>>>> Also the query over embedded triples wouldn’t find any people’s age
>>>>> that is not annotated, i.e. that is stated in a plain triple.
>>>> 
>>>> Of course not.
>>> 
>>> 
>>> "Of course" in a way ;-) Yes, if one asks for annotations, then the query shouldn’t return statements that are not annotated. However, at an early stage in exploring a graph - and those early stages are IMO those that need the most support from syntax - one is probably interested in statements both annotated or not. That’s what the query below does, as you correctly point out.
>>> 
>>>> The graph pattern of that query is explicitly asking for
>>>> embedded triples that have the dct:source annotation. The query to
>>>> always retrieve the age and optionally the source (if there is one)
>>>> needs to be written as follows (assuming the SPARQL* semantics as
>>>> defined in the paper!).
>>>> 
>>>> SELECT ?x ?age ?src
>>>> WHERE  {
>>>> ?x foaf:age ?age .
>>>> OPTIONAL {
>>>>    <<?x foaf:age ?age>> dct:source ?src .
>>>> }
>>>> }
>>> 
>>> Exactly. And the culmination of my long-ish mail [1] was to suggest that some syntactic sugar in support of this use case seems appropriate.
>>> 
>>> 
>>> Thanks again,
>>> Thomas
>>> 
>>> 
>>>> 
>>>>> [...]
>>>>> 
>>>>> [0] Olaf Hartig: Foundations of RDF* and SPARQL* - An Alternative
>>>>> Approach to Statement-Level Metadata in RDF, June 2017,
>>>>> http://olafhartig.de/files/Hartig_AMW2017_RDFStar.pdf

>>>>> [1]
>>>>> https://lists.w3.org/Archives/Public/public-rdf-star-wg/2024Aug/0032.html

>>> 
>>>

Received on Thursday, 15 August 2024 15:42:03 UTC