Re: [Rdfapi-php-interest] beginner SPARQL question

[Seaborne, A. <and...@hp...>]

John Vandenberg wrote:
> Hi,
> 
> I am trying to select a set of data out of a Mozilla extension
> install.rdf file.  I am using  SPARQL because it will be easy for
> developers to pick up and learn.
> 
> My problem is that when an optional entry doesnt exist (iconURL), none
> of the fields are returned.  This is the query I was trying to
> perform.
> 
> SELECT ?version, ?name, ?description, ?creator, ?icon
> WHERE (?x, <em:version>, ?version),
>       (?x, <em:name>, ?name),
>       (?x, <em:description>, ?description),
>       (?x, <em:creator>, ?creator),
>       (?x, <em:iconURL>, ?icon)
> USING em FOR <http://www.mozilla.org/2004/em-rdf#>
> 
> To work around this, I am individually selecting each optional piece
> of data.  Can this be improved on?
> 
> --
> John


That syntax is RDQL not SPARQL.

That query exactly translated is:

PREFIX  em:    <http://www.mozilla.org/2004/em-rdf#>

SELECT  ?version ?name ?description ?creator ?icon
WHERE
   { ?x  em:version      ?version ;
         em:name         ?name ;
         em:description  ?description ;
         em:creator      ?creator ;
         em:iconURL      ?icon .
   }

(Mechanical translation by program - but not a PHP program :-()

and adding optional for iconURL:

PREFIX  em:    <http://www.mozilla.org/2004/em-rdf#>

SELECT  ?version ?name ?description ?creator ?icon
WHERE
   { ?x  em:version      ?version .
     ?x  em:name         ?name .
     ?x  em:description  ?description .
     ?x  em:creator      ?creator .
     OPTIONAL { ?x em:iconURL      ?icon . }
   }

a little more neatly that is:

PREFIX  em:    <http://www.mozilla.org/2004/em-rdf#>
SELECT  ?version ?name ?description ?creator ?icon
WHERE
   { ?x  em:version      ?version ;
         em:name         ?name ;
         em:description  ?description ;
         em:creator      ?creator .
     OPTIONAL
       { ?x  em:iconURL  ?icon .}
   }

Hope that helps,

	Andy