Re: [dotNetRDF-bugs] Problems with SPARQL query

[<tom...@gm...>]

Thanks! Indeed works like charm.

Tom

January 7 2015 1:52 PM, "Rob Vesse" <rv...@do...> wrote: 
> Tom
> 
> This query hit a bug in our lazy evaluation implementation, turns out this
> query is one that looks like it can be lazily evaluated but can't in
> practise which causes us to do lazy evaluation anyway which is very slow
> when fully evaluating a BGP
> 
> I have already fixed this to instead fall back to normal BGP evaluation
> when this cases are hit and the query now completes fine.
> 
> As a workaround for previous versions you can disable lazy evaluation:
> 
> SparqlOptimiser.RemoveOptimiser(SparqlOptimiser.AlgebraOptimisers.Find(x
> => x.GetType().Equals(typeof(LazyBgpOptimiser)));
> 
> Bonus question:
> 
> FROM and FROM NAMED are only allowed by the SPARQL specification at the
> top level as they set the dataset for the entire query (including
> sub-queries)
> 
> Rob
> 
> On 06/01/2015 20:51, "tom...@gm..."
> <tom...@gm...> wrote:
> 
>> Hi Rob
>> 
>> I've been having some problems with a SPARQL query. Actually I extracted
>> it from a larger one, where it is a subquery. As a subquery I get some
>> inifinite loop and must terminate the process. On its own it times out. I
>> get the same results in all version from 0.7.2 onwards.
>> 
>> prefix hydra: <http://www.w3.org/ns/hydra/core#>
>> prefix dcterms: <http://purl.org/dc/terms/>
>> 
>> select ?member ?title
>> {
>> graph <http://localhost:17899/brochures>
>> {
>> <http://localhost:17899/brochures> hydra:member ?member .
>> ?member dcterms:title ?title
>> }
>> }
>> order by ?title
>> offset 0
>> limit 10
>> 
>> I've played with this query to identify the problem and I've got some
>> results. It works fine in either one case:
>> 
>> 1. Remove order
>> 2. Remove limit
>> 3. Replace GRAPH <> with FROM <>
>> 4. Remove the first triple pattern
>> 5. Replace two triple patterns with property path (and ditch ?member)
>> 
>> Key observation however is a modification to 3. If I use FROM <> but wrap
>> the triple pattern in a BGP I'm getting timeouts all the same.
>> 
>> My dataset can be downloaded from http://ge.tt/19Q3B582/v/0?c
>> 
>> As a bonus question, please tell me why is is not possible to use FROM
>> (NAMED) in subqueries? SPARQL specification or library limitation?
>> 
>> Thanks,
>> Tom
>> 
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> 
> _______________________________
> 
> Dive into the World of Parallel Programming! The Go Parallel Website,
> sponsored by Intel and developed in partnership with Slashdot Media, is your
> hub for all things parallel software development, from weekly thought
> leadership blogs to news, videos, case studies, tutorials and more. Take a
> look and join the conversation now. http://goparallel.sourceforge.net 
> _______________________________
> 
> dotNetRDF-bugs mailing list
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> https://lists.sourceforge.net/lists/listinfo/dotnetrdf-bugs