RE: Size a linked open data set

How about reformulating as:

select (count(?s) as ?c) where { select distinct ?s where { ?s ?p []} }

Which gives a result of 10515620 resources [1].

Regards,
John

[1] http://fr.dbpedia.org/sparql?default-graph-uri=&query=select+%28count%28%3Fs%29+as+%3Fc%29+where+%7B+select+distinct+%3Fs+where+%7B+%3Fs+%3Fp+%5B%5D%7D+%7D&format=text%2Fhtml&timeout=0&debug=on



-----Original Message-----
From: Hugh Williams [mailto:hwilliams@openlinksw.com] 
Sent: Wednesday, July 06, 2016 3:15 PM
To: Jean-Claude Moissinac <jean-claude.moissinac@telecom-paristech.fr>
Cc: public-lod <public-lod@w3.org>
Subject: Re: Size a linked open data set

Hi Jean-Claude,

The "select count(distinct ?r) where { ?r ?p ?l }” query is expensive in terms of database resources and would result in a huge hash table being creating to try and service it which is causing it to timeout based on the settings on the instance by whoever maintains it.

On http://dbpedia.org/sparql the original canonical English DBpedia endpoint OpenLink Software hosts, we provide preloaded VOID datasets, such that they don’t have to be queried each time, see http://dbpedia.org/void/Dataset , but the French DBpedia instance does not appear to have this ie http://fr.dbpedia.org/void/Dataset 

Best Regards
Hugh Williams
Professional Services
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> On 6 Jul 2016, at 12:49, Jean-Claude Moissinac <jean-claude.moissinac@telecom-paristech.fr> wrote:
> 
> Hello
> 
> In my work, I need to know the number of distinct resources in a dataset.
> For example, with dbpedia-fr, I'm trying
> select count(distinct ?r) where { ?r ?p ?l } 
> 
> And I'm always getting a timeout error message
> While with
> select count(?r) where { ?r ?p ?l } 
> I'm getting
> 185404575
> 
> Is it a good way to know about such size?
> 
> --
> Jean-Claude Moissinac
>

Received on Wednesday, 6 July 2016 13:56:07 UTC