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Re: The truth about SPARQL Endpoint availability

From: Hugh Glaser <hg@ecs.soton.ac.uk>
Date: Sun, 6 Mar 2011 12:02:04 +0000
To: Tim Berners-Lee <timbl@w3.org>
CC: Bill Roberts <bill@swirrl.com>, Linked Data community <public-lod@w3.org>
Message-ID: <EMEW3|9c677960e3874ceba6a734af06f2d31dn25C2Z02hg|ecs.soton.ac.uk|4B563980-7A9E-44FF-988E-AC98F3CD4752@ecs.soton.ac.uk>
Yes, I was puzzling over this.
And then what other useful things might be special-cased.
(classes?, even a dump of rdfs:label?)

But it sort of sticks in the craw to do that.
And I keep coming back to the fact that there is already a way of doing this in the Linked Data world.
If you have the voiD description in your endpoint, then it all just works.
And it can be queried or browsed, etc.

So for example (in our case) querying http://southampton.rkbexplorer.com/sparql/ with
{?s void:sparqlEndpoint http://southampton.rkbexplorer.com/sparql/}
gives
?s = http://southampton.rkbexplorer.com/id/void
And bingo!
Browse the store metadata as LD or SPARQL to your heart's content, as you would with any other data we offer from that store.
And whatever else metadata about the store that is wanted can be proposed as different vocabs or extensions to voiD.

One thing I am puzzling over, though:
Should http://southampton.rkbexplorer.com/sparql/ be Linked Data?
Currently if you ask for RDF we give "406 Not Acceptable".
It might be helpful to 303 to an RDF description; and if so, would it look different from the voiD description?
Or certainly somehow getting back an rdfs:seeAlso would be valid.
Or is this already sorted out somewhere that I have missed?
(I told you I'm not a voiD guru :-) )

Best
Hugh


On 6 Mar 2011, at 11:20, Tim Berners-Lee wrote:

> Maybe the count of triples should be special-cased in the sparql server code,
> spotted on input and the store size returned.
> if it is reasonable for the endpoint to keep track of the size of its store.
> (Do they anyway?)
> 
> Tim
> 
> On 2011-03 -05, at 11:58, Bill Roberts wrote:
> 
>> Thanks Hugh - as someone running a couple of SPARQL endpoints, I'd certainly prefer if people don't run a global count too often (or at all). It is indeed something that makes typical SPARQL implementations work very hard.
>> 
>> But it's a good reminder we should provide an alternative and i'll look into providing triple counts in voiD.
>> 
>> Bill
>> 
>> 
>> On 5 Mar 2011, at 15:14, Hugh Glaser wrote:
>> 
>>> Hi,
>>> On 5 Mar 2011, at 14:22, Andrea Splendiani wrote:
>>> 
>>>> Hi,
>>>> 
>>>> I think it depends on the store, I've tried some (from the endpoint list) and some returns a answer pretty quickly. Some doesn't and some doesn't support count.
>>>> However, one could have this information only for the stores that answers the count query, no need to try all time.
>>> I am happy for a store implementor or owner to disagree, but I find it very unlikely that the owner of a store with a decent chunk of data (> 1M triples, say) would be happy for someone to keep issuing such a query, even if they did decide to give enough resources to execute it.
>>> I would quickly blacklist such a site.
>>>> 
>>>> VoID:
>>>> is this a good query:
>>>> select * where {?s <http://rdfs.org/ns/void#numberOfTriples> ?o } 
>>> 
>>> I'm no SPARQL or voiD guru, but I think you need a bit more wrapping in the scovo stuff, so more like:
>>> 
>>> SELECT DISTINCT ?endpoint ?uri ?triples ?uris WHERE
>>>         { ?ds a void:Dataset .
>>>           ?ds void:sparqlEndpoint ?uri .
>>>           ?ds rdfs:label ?endpoint .
>>>           ?ds void:statItem [ scovo:dimension void:numberOfTriples ; rdf:value  ?triples ] .
>>>        }
>>> 
>>> Try it at
>>> http://kwijibo.talis.com/voiD/
>>> or
>>> http://void.rkbexplorer.com/
>>> 
>>> I guess Pierre-Yves might like to enhance his page by querying a voiD store to also give basic stats.
>>> Or someone might like to do a store reporter that uses (a) voiD endpoint(s) plus Pierre-Yves's data (he has a SPARQL endpoint), to do so.
>>> And maybe the CKAN endpoint would have extra useful data as well.
>>> A real Semantic Web application that queried more than one SPARQL endpoint - now that would be a novelty!
>>> Fancy the challenge, it is the weekend?! :-)
>>> 
>>> ciao
>>> Hugh
>>> 
>>>> 
>>>> it doesn't seem viable if so.
>>>> 
>>>> ciao,
>>>> Andrea
>>>> 
>>>> 
>>>> Il giorno 05/mar/2011, alle ore 13.49, Hugh Glaser ha scritto:
>>>> 
>>>>> NIce idea, but,... :-)
>>>>> 
>>>>> SELECT (count(*) as ?c) WHERE {?s ?p ?o}
>>>>> 
>>>>> is a pretty anti-social thing to do to a store.
>>>>> At best, a store of any size will spend a while thinking, and then quite rightly decide they have burnt enough resources, and return some sort of error.
>>>>> 
>>>>> For a properly maintained site, of course, the VoiD description will give lots of similar information.
>>>>> Best
>>>>> Hugh
>>>>> 
>>>>> On 5 Mar 2011, at 13:06, Andrea Splendiani wrote:
>>>>> 
>>>>>> Hi, very nice!
>>>>>> I have a small suggestion:
>>>>>> 
>>>>>> why don't you ask "count(*) where {?s ?p ?o}" to the endpoint ?
>>>>>> Or ask for the number of graphs ?
>>>>>> Both information, number of triples and number of graphs, if logged and compared over time, can give a practical view of the liveliness of the content of the endpoint.
>>>>>> 
>>>>>> best,
>>>>>> Andrea Splendiani
>>>>>> 
>>>>>> 
>>>>>> Il giorno 28/feb/2011, alle ore 18.55, Pierre-Yves Vandenbussche ha scritto:
>>>>>> 
>>>>>>> Hello all,
>>>>>>> 
>>>>>>> you have already encountered problems of SPARQL endpoint accessibility ?
>>>>>>> you feel frustrated they are never available when you need them?
>>>>>>> you develop an application using these services but wonder if it is reliable?
>>>>>>> 
>>>>>>> Here is a tool [1] that allows you to know public SPARQL endpoints availability and monitor them in the last hours/days. 
>>>>>>> Stay informed of a particular (or all) endpoint status changes through RSS feeds.
>>>>>>> All availability information generated by this tool is accessible through a SPARQL endpoint.
>>>>>>> 
>>>>>>> This tool fetches public SPARQL endpoints from CKAN  open data. From this list, it runs tests every hour for availability.
>>>>>>> 
>>>>>>> [1] http://labs.mondeca.com/sparqlEndpointsStatus/index.html
>>>>>>> [2] http://ckan.net/
>>>>>>> 
>>>>>>> Pierre-Yves Vandenbussche.
>>>>>> 
>>>>>> Andrea Splendiani
>>>>>> Senior Bioinformatics Scientist
>>>>>> Centre for Mathematical and Computational Biology
>>>>>> +44(0)1582 763133 ext 2004
>>>>>> andrea.splendiani@bbsrc.ac.uk
>>>>>> 
>>>>>> 
>>>>>> 
>>>>> 
>>>>> -- 
>>>>> Hugh Glaser,  
>>>>>          Intelligence, Agents, Multimedia
>>>>>          School of Electronics and Computer Science,
>>>>>          University of Southampton,
>>>>>          Southampton SO17 1BJ
>>>>> Work: +44 23 8059 3670, Fax: +44 23 8059 3045
>>>>> Mobile: +44 78 9422 3822, Home: +44 23 8061 5652
>>>>> http://www.ecs.soton.ac.uk/~hg/
>>>>> 
>>>>> 
>>>> 
>>>> Andrea Splendiani
>>>> Senior Bioinformatics Scientist
>>>> Centre for Mathematical and Computational Biology
>>>> +44(0)1582 763133 ext 2004
>>>> andrea.splendiani@bbsrc.ac.uk
>>>> 
>>>> 
>>>> 
>>> 
>>> -- 
>>> Hugh Glaser,  
>>>            Intelligence, Agents, Multimedia
>>>            School of Electronics and Computer Science,
>>>            University of Southampton,
>>>            Southampton SO17 1BJ
>>> Work: +44 23 8059 3670, Fax: +44 23 8059 3045
>>> Mobile: +44 78 9422 3822, Home: +44 23 8061 5652
>>> http://www.ecs.soton.ac.uk/~hg/
>>> 
>>> 
>>> 
>> 
>> 
>> 
> 

-- 
Hugh Glaser,  
              Intelligence, Agents, Multimedia
              School of Electronics and Computer Science,
              University of Southampton,
              Southampton SO17 1BJ
Work: +44 23 8059 3670, Fax: +44 23 8059 3045
Mobile: +44 78 9422 3822, Home: +44 23 8061 5652
http://www.ecs.soton.ac.uk/~hg/
Received on Sunday, 6 March 2011 12:03:12 UTC

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