Re: Making querying of annotations optional

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. 

. 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 15:21:52 UTC