Re: Different encoding for RDF-star queries as S-Expressions with Jena

On 21/01/2022 21:19, Gregg Kellogg wrote:
>> On Jan 21, 2022, at 9:38 AM, Andy Seaborne <andy@seaborne.org 
>> <mailto:andy@seaborne.org>> wrote:
>>
>> Jena parses and evaluates Daniel's original example - it is using a 
>> (triple) as an expression. SPARQL-star TRIPLE.
>>
>> The two expression are not identical - one has quoted triple term <<>> 
>> pattern, the other has an expression that evaluates to a quoted triple 
>> -the TRIPLE(expr, expr, expr) function in SPARQL-star.
>>
>> So there are three cases:
>>
>> 1 : triple pattern - 3-tuple of RDF-terms/variables.
>> 2 : quoted triple pattern, an RDF term + may have variables
>> 3 : TRIPLE/3 function - arguments are expressions.
>>
>> triple != quoted triple.  strict typing :-)
> 
> Within Ruby RDF, the representation is equivalent, with the TRIPLE/3 
> function being just a constructor.
> 
>> On 20/01/2022 22:10, Gregg Kellogg wrote:
>> > While, Ruby RDF outputs:
>> >
>> > (prefix ((:<http://bigdata.com <http://bigdata.com/>>)
>> >           (foaf:<http://xmlns.com/foaf/0.1/ <http://xmlns.com/foaf/0.1/>>)
>> >           (ex:<http://example.org/ <http://example.org/>>))
>> >   (project (?age ?c)
>> >    (bgp
>> >     (triple ?bob foaf:name "Bob")
>> >     (triple (triple ?bob foaf:age ?age) ex:certainty ?c))))
>> >
>> > I’m not sure if this is intentional on Andy’s part, as  `triple << ?bob foaf:age ?age >> ex:certainty ?c)` doesn’t really look like an S-Expression to my eyes,
>>
>> "intention" is too strong :-)
>>
>> <<>> is another kind of RDF term, like <uri> or "string". I'd happily 
>> swap to a ()-form. It's messy and special case to parse.
>>
>> There again, parsing <<>> is a bit fiddly. Nested <<>> is allowed.
>>
>> Without a separate word, those three uses of (triple) have context 
>> sensitive meaning and have to be coded around at each usage site which 
>> is not nice.
>>
>> A word for quoted triple? (qtriple)?
> 
> “qtriple” seems like a good compromise, which should simplify the 
> to_sparql implementation. I’ll give that a shot.

I didn't expect SSE to have any use outside Jena.

https://issues.apache.org/jira/browse/JENA-2259

> 
> Thanks for your input, Andy.

NP.

> 
> Gregg
> 
>>
>> On 21/01/2022 11:13, Daniel Hernandez wrote:
>>> Hi all,
>>> Gregg Kellogg writes:
>>>> Of course, there is no real standard for expressing queries as
>>>> s-expressions, but Ruby RDF generally follows Jena. (Creating a
>>>> normative S-Expression representation would be interesting, though).
>>> I agree on that a normative for S-Expressions would help for
>>> interoperability.
>>>> I’m not sure if this is intentional on Andy’s part, as `triple << ?bob
>>>> foaf:age ?age >> ex:certainty ?c)` doesn’t really look like an
>>>> S-Expression to my eyes, and the “triple” expression has already been
>>>> established, but using that embedded triple expression made the most
>>>> sense to me. It does lead to some complications in re-serializing, as
>>>> SPARQL-star does have a TRIPLE function, which gets the same
>>>> representation in Ruby RDF, and distinguishing between their use took
>>>> some doing, but internally, it’s never been an issue.
>>> Gregg, I agree with you on that the notation <<...>> doesn't look as
>>> look as an S-Expression.  Hence, this notation requires implementing an
>>> additional type of parenthesis.  Indeed, if S-Expressions allow for the
>>> notation <<...>>, then it is also needed to support nested triple
>>> expressions, for example << << ?s ?p ?o >> ?q ?r >> ?s ?v.
>>
>> Yes. It does.
>>
>>>> I wasn’t able to get qparse to parse either form of S-Expression, but
>>>> that’s likely an operator error.
>>
>> qparse does not parse SSE. It is only an output format.
>>
>>> I have tested how Jena parse both forms, and seems that Jena support
>>> both forms. It translates << ?s ?p ?o >> as an embedded triple
>>> expression << ?s ?p ?o >>, whereas (triple ?s ?p ?o) is translated as
>>> the triple function triple(?s, ?p, ?o).
>>> Daniel
>

Received on Friday, 21 January 2022 22:51:14 UTC