Hi Eric,
I agree with much of what you are saying but I think the important point is
that "Construct statements make a graphs of triples". Graphs don't have an
order. If you imagine that the CONSTRUCT pipeline is
SELECT a set of bindings (which could be ordered)
==> send these to the CONSTRUCT template to be converted into a graph
any ordering would be immediately lost in the second step.
OTOH, I can see where you might want to be able to use information in the
SELECTed results in the template. If SPARQL had a SEQUENCE function which
returned, for example, the next xsd:int starting at 0, you could do something
like:
CONSTRUCT {
?a ex:foo ?b .
?a ex:solutionNumber ?seq .
} WHERE {
?a ex:bar ?b .
BIND(SEQUENCE() AS ?seq)
} ORDER BY ?b
Is this the sort of thing you'd be interested in? I can certainly imagine that
it would be handy.
On Oct 18, 2012, at 6:45 PM, Erich Bremer <[email protected]> wrote:
> Hi Gary,
>
> Construct statements make a graphs of triples representing information.
> Construct statements can be used to manipulate, subset, and create new data
> derived from existing data. Temporal and sequential information being
> important things in this world, it would make perfect sense to be able to do
> a ORDER BY on a construct statement so that connecting triples can be
> generated to make linked lists of ordered information. The problem is that
> there is no way to reference the prior/next solution of the where clause in
> the construct statement to create the appropriate triple pattern.
> Triple/quad stores do order information in that triples/quads are indexed by
> their SPOG components to allow for faster processing of graph patterns.
> Although what I am looking for could be achieved in code, it would be
> beneficial to add a SPARQL feature allowing the referencing of a prior/next
> solution. The use cases exist and I don't see it being particularly difficult
> to implement -imho. - Erich
>
> Erich Bremer
> http://www.ebremer.com
>
> On 10/17/12 10:22 AM, Gary King wrote:
>> Hi Erich,
>>
>>> There doesn't seem to be anyway to create a SPARQL construct statement like
>>> the following:
>>>
>> I believe that the reasoning is that CONSTRUCT makes a _set_ of triples and
>> sets don't have an order. I.e., a triple-store is an unordered collection
>> and that it what CONSTRUCT constructs :-).
>>
>>> but I did not get anything that would work or seem remotely efficient. If
>>> this is the case, why have order by in a construct statement at all if one
>>> cannot capture this information as triples?
>>
>> The ORDER clause in your example is essentially a no-op. Obviously, however,
>> it would be important if you also had a LIMIT.
>>
>> HTH,
>> --
>> Gary Warren King, metabang.com
>> Cell: (413) 559 8738
>> Fax: (206) 338-4052
>> gwkkwg on Skype * garethsan on AIM * gwking on twitter
>>
>
>
--
Gary Warren King, metabang.com
Cell: (413) 559 8738
Fax: (206) 338-4052
gwkkwg on Skype * garethsan on AIM * gwking on twitter
