Re: CONSTRUCT an RDF Datest

good afternoon;

> On 2015-12-06, at 00:16, Miguel <miguel.ceriani@gmail.com> wrote:
> 
> […]
> Generally, I guess we must consider all the possible different ways in which the template of the CONSTRUCT subquery may be matched by the corresponding BGPs of the "main query".
> This can be done but the query will generally grow (combinatorially) in size.

the first-order question was sufficiency.
which depends on whether the projection function could be alpha-converted for in-line substitution.
which, as you point out, below, would not be possible for kleen start paths.
so, agreed.

on the other hand, is the combinatorics argument any different  than that which applies to sparql’s general deficiency with respect to sub-expression (bgp) abstraction.
for which would it not be better to advance the algebra’s capacity in general - that is to extend and abstract both solution field generation and target graph generation in the form of the requisite operations, rather than making do with extending the dataset definition only?

> 
> Furthermore, if property paths are allowed, the would-be-language using CONSTRUCT subqueries is strictly more powerful than the one without.
> The following query cannot be written in SPARQL 1.1
> 
> SELECT ?paper ?influentialPaper
> FROM {
>     CONSTRUCT { ?citingPaper ex:isJournalAndCites ?citedPaper }
>     WHERE {
>         ?citingPaper a ex:JournalPaper.
>         ?citingPaper ex:cites ?citedPaper.
>     }
> }
> WHERE { ?paper ex:isJournalAndCites* ?influentialPaper }
> 
> This is just to say that I don't think CONSTRUCT subqueries in FROM/FROM NAMED can be considered completely "subsumed" by the subquery forms available in SPARQL 1.1.
> 
> Best Regards,
> Miguel
> 
> 
> Il giorno sab 5 dic 2015 alle ore 22:35 james anderson <james@dydra.com <mailto:james@dydra.com>> ha scritto:
> good evening;
> 
> 
>> On 2015-12-05, at 21:30, Tara Athan <taraathan@gmail.com <mailto:taraathan@gmail.com>> wrote:
>> 
> 
>> I found this paper http://ceur-ws.org/Vol-749/paper19.pdf <http://ceur-ws.org/Vol-749/paper19.pdf> which proposes allowing CONSTRUCT to be nested within FROM and FROM NAMED. I would be interested to know if any engines have implemented this as an extension.
>> 
>> 
>> I gather that this was considered in the development of SPARQL 1.1, but not adopted: http://www.w3.org/2009/sparql/track/issues/7 <http://www.w3.org/2009/sparql/track/issues/7>
>> I don't understand the justification of the closure
>> > ISSUE-7
>> > CONSTRUCT & DESCRIBE queries in FROM [NAMED]?    
>> >   ??
>> >   CONSTRUCT not needed if bNodes can be introduced by constructor.
>> 
>> I looked for emails that explain how introducing bNodes by a constructor can take the place of composition of CONSTRUCT ( I can't imagine how this can be the case, but am willing to read the arguments...) but I can't find it.
>> 
>> As background, the usecase I am considering is a CONSTRUCT view that creates a virtual RDF dataset (using the Construct Quad extension) and then exposes this virtual view to the user for further queries (which could be CONSTRUCT, SELECT, or whatever.) This would have the effect of inserting the CONSTRUCT view into the FROM clause of the users query.
> 
> 
> angles/gutierrez proposes three forms of subquery.
> sparql 1.1 includes the second and third forms.
> the first one (from / from named) is less effective then the second, as it is not possible to place the results.
> they would have to be merged into the default graph or made available as a named graph.
> the subselect form allows to accomplish the same result as that which would be produced by the generated dataset combined with the eventual graph pattern in the query itself.
> 
> taking, for instance, their example 2:
> 
> SELECT ?M1 ?M2
> FROM  <http://.../people.rdf <http://.../people.rdf>>
> FROM ( CONSTRUCT { ?A1 co-author ?A2 } 
>        FROM <http://.../biblio.rdf <http://.../biblio.rdf>>
>        WHERE { ?Pub author ?A1 .
>                ?Pub author ?A2 .
>                FILTER ( !(?A1 = ?A2) ) }
>      )
> WHERE { ?P1 co-author ?P2 . ?P1 mail ?M1 . ?P2 mail ?M2 }
> 
> would be
> 
> PREFIX : <http:/example.org/ <http://example.org/>>
> SELECT ?M1 ?M2
> FROM  <http://.../people.rdf <http://.../people.rdf>>
> FROM NAMED <http://.../biblio.rdf <http://.../biblio.rdf>>
> WHERE { { SELECT ?P1 ?P2
>           WHERE { GRAPH <http://.../biblio.rdf <http://.../biblio.rdf>>
>                   { ?Pub :author ?A1 .
>                     ?Pub :author ?A2 .
>                      FILTER ( !(?A1 = ?A2) ) } } }
>          ?P1 :mail ?M1 .
>          ?P2 :mail ?M2 }
> 
> best regards, from berlin,
> 
> 
> 
> ---
> james anderson | james@dydra.com <mailto:james@dydra.com> | http://dydra.com <http://dydra.com/>
> 
> 
> 
> 
> 

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james anderson | james@dydra.com | http://dydra.com