[redland-dev] Status of OPTIONAL

[Richard Newman]

Try nesting them.

PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT ?name ?mbox ?hpage
WHERE  { ?x foaf:name  ?name .
    OPTIONAL {
      ?x foaf:mbox ?mbox .
      OPTIONAL { ?x foaf:homepage ?hpage }
    }
}

The semantics should be the same, and it might work (that's a problem  
with a few RDF toolkits).

-R


On  20 Mar 2007, at 1:06 PM, Knud Hinnerk Möller wrote:

> Hi,
>
> I know OPTIONAL doesn't work properly yet - do you have any idea  
> when it will? Single OPTIONALS seem to work fine, but multiples  
> don't seem to work. In particular, this query from the SPARQL spec  
> seems to work:
>
> PREFIX foaf: <http://xmlns.com/foaf/0.1/>
> SELECT ?name ?mbox
> WHERE  { ?x foaf:name  ?name .
>    OPTIONAL { ?x  foaf:mbox  ?mbox }
> }
>
> But this one doesn't:
>
> PREFIX foaf: <http://xmlns.com/foaf/0.1/>
> SELECT ?name ?mbox ?hpage
> WHERE  { ?x foaf:name  ?name .
>    OPTIONAL { ?x foaf:mbox ?mbox } .
>    OPTIONAL { ?x foaf:homepage ?hpage }
> }
>
> The first OPTIONAL is ignored, and the query evaluates identically to:
>
> PREFIX foaf: <http://xmlns.com/foaf/0.1/>
> SELECT ?name ?mbox ?hpage
> WHERE  { ?x foaf:name  ?name .
>    ?x foaf:mbox ?mbox .
>    OPTIONAL { ?x foaf:homepage ?hpage }
> }
>
> In the meantime, are there any code examples that show how to do a  
> workaround programmatically?
>
> Cheers,
> Knud
> -------------------------------------------------
> Knud Möller, MA
> +353 - 91 - 495086
> Digital Enterprise Research Institute
>   National University of Ireland, Galway
> Institiúid Taighde na Fiontraíochta Digití
>   Ollscoil na hÉireann, Gaillimh
>
>
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