[redland-dev] Status of OPTIONAL

[Knud Hinnerk Möller]

Yes, that's what I thought. Anyway, it's not really urgent for me (I  =

did a programmatic workaround now). Still, I would be cool to have  =

it! :-)

Cheers,
Knud

Am 21.03.2007 um 09:41 schrieb Seaborne, Andy:

> -------- Original Message --------
>> From: Richard Newman <>
>> Date: 20 March 2007 20:10
>>
>> 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
>
> The semantics aren't the same!
>
> Pattern 1:
>
> WHERE  { ?x foaf:name  ?name .
>     OPTIONAL { ?x foaf:mbox ?mbox } .
>     OPTIONAL { ?x foaf:homepage ?hpage } }
>
>
> Pattern 2:
>
>     WHERE  { ?x foaf:name  ?name .
>      OPTIONAL {
>         ?x foaf:mbox ?mbox .
>         OPTIONAL { ?x foaf:homepage ?hpage }
>
> In pattern 2, ?hpage can only be bound if ?mbox is also bound.
> If ?mbox does not match, it will fail the outer OPTIONAL and so the  =

> inner one, with ?hpage, will not return a binding regardless of  =

> whether the inner pattern matches.
>
> In pattern 1, one, both or neither of ?mbox, ?hpage can be bound.
>
> 	Andy
>
>
>>
>>
>> On  20 Mar 2007, at 1:06 PM, Knud Hinnerk M=F6ller 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 M=F6ller, MA
>>> +353 - 91 - 495086
>>> Digital Enterprise Research Institute
>>>   National University of Ireland, Galway Institi=FAid Taighde na
>>>   Fiontra=EDochta Digit=ED Ollscoil na h=C9ireann, Gaillimh
>>>
>>>
>>> _______________________________________________
>>> redland-dev mailing list
>>> redland-dev at lists.librdf.org
>>> http://lists.librdf.org/mailman/listinfo/redland-dev
>>
>> _______________________________________________
>> redland-dev mailing list
>> redland-dev at lists.librdf.org
>> http://lists.librdf.org/mailman/listinfo/redland-dev
>

-------------------------------------------------
Knud M=F6ller, MA
+353 - 91 - 495086
Digital Enterprise Research Institute
   National University of Ireland, Galway
Institi=FAid Taighde na Fiontra=EDochta Digit=ED
   Ollscoil na h=C9ireann, Gaillimh


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