Re: getting the query from an SXP expression

Thanks, Aymeric. That was my vague recollection from some time ago. Glad that it lives on.

Gregg Kellogg

Sent from my iPad

> On Dec 2, 2021, at 3:46 AM, Aymeric Brisse <aymeric.brisse@gmail.com> wrote:
> 
> 
> Hello,
> 
> I implemented such a system a few years ago but didn't make a PR since I found it was too hackish for open source standards.
> 
> But it currently supports 47 SPARQL operators so I think it can be a good start to work on a better version. I will look at the Jena implementation to see how they did it.
> 
> I have created a gist here : https://gist.github.com/abrisse/8f9893549f00e94c25cbe0bea93e532d
> 
> For example :
> 
> query = %q{
> PREFIX rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>
> PREFIX pmcore:<http://www.perfect-memory.com/ontology/pmcore/1.0#>
> 
> CONSTRUCT
> WHERE {
>   ?uri rdf:type pmcore:Movie ; pmcore:contains ?element
> }
> }
> 
> puts ::SPARQL::Grammar.parse(query).sparql_fragment
> 
> #  generates the following expanded version :
> 
> PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
> PREFIX pmcore: <http://www.perfect-memory.com/ontology/pmcore/1.0#>
> CONSTRUCT {
>   ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.perfect-memory.com/ontology/pmcore/1.0#Movie> .
>   ?uri <http://www.perfect-memory.com/ontology/pmcore/1.0#contains> ?element .
> }
> WHERE {
>   ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.perfect-memory.com/ontology/pmcore/1.0#Movie> .
>   ?uri <http://www.perfect-memory.com/ontology/pmcore/1.0#contains> ?element . 
> }
> 
> Cheers,
> Aymeric
> 
> 
>> On Thu, Dec 2, 2021 at 12:06 PM Daniel Hernandez <daniel@degu.cl> wrote:
>> 
>> Thank you for your answer.  I think now I understand better the role
>> that play SPARQL::Grammar, SPARQL::Algebra, and SPARQL::Client (please
>> fix me if I am wrong).  The first two allow for creating instances of an
>> algebraic expression from a string (using either the SPARQL or the SSE
>> grammars), and can be translated to SSE.  The last provides a DSL to
>> define queries, and does not care about the SPARQL algebra.
>> 
>> Gregg, I am going to implement the hypothetical method inside my app,
>> for some few cases, and then I am going to share the code to see if this
>> is useful for the general implementation.
>> 
>> Daniel Hernández
>> 
>> Gregg Kellogg <gregg@greggkellogg.net> writes:
>> 
>> > The approach Jena takes probably makes it better to have such a mechanism be part of the core sparql gem, not restricted to sparq-client. I created an issue for it in the sparql repo [1].
>> >
>> > A hypothetical SPARQL::Algebra::Operator#to_sparql method might method that could be used to do this.
>> >
>> > Gregg Kellogg
>> > gregg@greggkellogg.net
>> >
>> > [1] https://github.com/ruby-rdf/sparql/issues/38 <https://github.com/ruby-rdf/sparql/issues/38>
>> >
>> >> On Dec 1, 2021, at 1:45 PM, Gregg Kellogg <gregg@greggkellogg.com> wrote:
>> >>
>> >> Thanks Andy, that’s what I was looking for. Could be ported to Ruby reasonably.
>> >>
>> >> Gregg Kellogg
>> SPARQL::Algebra::Operator>> Sent from my iPhone
>> >>
>> >>> On Dec 1, 2021, at 1:13 PM, Andy Seaborne <andy@seaborne.org> wrote:
>> >>>
>> >>> 
>> >>>
>> >>>> On 01/12/2021 20:30, Gregg Kellogg wrote:
>> >>>> (Sorry, previous reply was inadvertently not reply all).
>> >>>> I recall some discussion about this several years ago, and it may be possible, at least in limited cases. I’m also not aware of any other platforms which use SPARQL S-Expressions which do any de-compilation.
>> >>>
>> >>> Jena tries to - it's quite pragmatic:
>> >>>
>> >>> https://github.com/apache/jena/blob/main/jena-arq/src/main/java/org/apache/jena/sparql/algebra/OpAsQuery.java
>> >>>
>> >>>   Andy
>> >>>
>> >>>> I had thought that this would be good for the sparql-client gem, which could take an SSE input and turn it into SPARQL Grammar, and for trivial use cases it shouldn’t be too difficult to do, but I never pursued the issue. I’d be happy for someone to look into this further and maybe create a PR, even if it is only a partial solution. To not get lost, it might be good to create an issue in https://github.com/ruby-rdf/sparql-client/issues <https://github.com/ruby-rdf/sparql-client/issues> so that we don’t loose discussions again.
>> >>>> Typically, the SXP is intended for optimization and execution, not to round trip back to the sparql grammar. There may be some other work on this, but I’m not aware of any. There’s quire a bit of activity in http://rdf.js.org/query-spec/ <http://rdf.js.org/query-spec/>c <https://github.com/rdfjs/query-spec> for that JavaScript community, and there may be some work there that could be leveraged.
>> >>>> In general, I would welcome more collaboration on the Ruby RDF/SPARQL gems, which have been fairly quiet for a while, other than for basic maintenance. I am planning a 3.2 release, but that will mostly be to maintain dependencies and minimum Ruby versions.
>> >>>> Gregg Kellogg
>> >>>> gregg@greggkellogg.net <mailto:gregg@greggkellogg.net>
>> >>>>>> On Dec 1, 2021, at 6:35 AM, Daniel Hernandez <daniel@degu.cl <mailto:daniel@degu.cl>> wrote:
>> >>>>>
>> >>>>>
>> >>>>> In the previous example I made a mistake it is `parse` instead of `for`
>> >>>>> (the question is the same).
>> >>>>>
>> >>>>> Daniel Hernandez <daniel@degu.cl <mailto:daniel@degu.cl>> writes:
>> >>>>>
>> >>>>>> Hi all,
>> >>>>>>
>> >>>>>> I am trying to get the SPARQL query of a sse expression.
>> >>>>>> For instance, if I have
>> >>>>>>
>> >>>>>> exp = SPARQL::Algebra::Expression.for "(project (?x) (bgp (triple ?s ?p ?x)))"
>> >>>>>>
>> >>>>>> then I want the string "SELECT ?x WHERE {?s ?p ?x}".
>> >>>>>>
>> >>>>>> Thanks,
>> >>>>>> Daniel
>> >>>>>
>> >>>
>>