Re: Named graphs Fuseki/TDB

Andy Seaborne Thu, 13 Oct 2011 12:11:29 -0700

On 13/10/11 14:01, Paolo Castagna wrote:

Hi Chris


Chris Clarke wrote:

I'm trying to load some data into named graphs in TDB and then query back with 
Fuseki. Perhaps I am doing something ridiculously stupid here having never 
worked with quads and named graphs before....

For my test case I have about 5 million quads I am trying to load into one 
named graph, here is a sample of some:

<http://example.com/sections/FFF9AF7F-54DF-53A5-E2A1-E08F4F7C270F>  
<http://www.w3.org/1999/02/22-rdf-syntax-ns#_8>  
<http://example.com/items/6226E191-0A32-F348-8F38-AABDBC73EE83>   <http://example.com/>  .
<http://example.com/sections/FFF9AF7F-54DF-53A5-E2A1-E08F4F7C270F>  
<http://www.w3.org/1999/02/22-rdf-syntax-ns#_9>  
<http://example.com/items/0FBFA283-11EB-1A04-1F68-F8B36E03F932>   <http://example.com/>  .
<http://example.com/sections/FFF9AF7F-54DF-53A5-E2A1-E08F4F7C270F>  
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>  
<http://purl.org/vocab/resourcelist/schema#Section>   <http://example.com/>  .
<http://example.com/sections/FFF9AF7F-54DF-53A5-E2A1-E08F4F7C270F>  
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>  
<http://www.w3.org/1999/02/22-rdf-syntax-ns#Seq>   <http://example.com/>  .

What I would expect is that each of these quads get loaded into a graph 
named<http://example.com/>

Using tdbloader2, I successfully loaded these into a fresh TDB database 
location.

Start Fuseki 0.2.1-snapshot using this manifest:

@prefix tdb:<http://jena.hpl.hp.com/2008/tdb#>  .
@prefix rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>  .
@prefix rdfs:<http://www.w3.org/2000/01/rdf-schema#>  .
@prefix ja:<http://jena.hpl.hp.com/2005/11/Assembler#>  .
@prefix tdb:<http://jena.hpl.hp.com/2008/tdb#>  .

[] ja:loadClass "com.hp.hpl.jena.tdb.TDB" .
tdb:DatasetTDB  rdfs:subClassOf  ja:RDFDataset .
tdb:GraphTDB    rdfs:subClassOf  ja:Model .

  <#dataset>  rdf:type      tdb:DatasetTDB ;
      tdb:location "/tmp/DBQ-test" ;
      .

I try and submit this test query via the Fueski web interface 
(http://myfusekiserver:3030/sparql.jsp):

select count(?s)
from named<http://example.com/>
where {?s ?p ?o}

Fuseki says:

Error 400: Query may not include a dataset description (FROM/FROM NAMED)


We have recently seen Tim asking a similar question (with a similar error).
This is the relevant thread: http://markmail.org/message/igbs7uxlx5xtooyz

As a work around, you could use this as an alternative:

SELECT COUNT(?s)
{
   GRAPH<http://example.com/
   {
     ?s ?p ?o
   }
}

Does this work for you?


It's not a workaround.  That's how, in SPARQL, you access a named graph.

The email referred to above is about changing the dataset the query runsover to a subset of the graphs in the store. See the TDB wiki aboutdynamic datasets.

http://www.openjena.org/wiki/TDB/DynamicDatasets

Using GRAPH is better for access to a specific graph.  Only if you want to
1/ Have a default graph that is the union of a set of other graphs
2/ restrict the visible named graphs

do you need FROM/FROM NAMED with TDB. It's a specialized use.

Fuseki currently does pass through the FROM/FROM NAMED.

        Andy



Fuseki - version 0.2.1-SNAPSHOT (Date: 2011-09-08T16:38:26+0000)

Aside: I ran tdbstats on the location where I loaded the quads, I got the 
results I would expect in the stats.opt file:

(stats
   (meta
     (timestamp 
"2011-10-13T10:22:47.351+00:00"^^<http://www.w3.org/2001/XMLSchema#dateTime>)
     (run@ "2011/10/13 10:22:47 UTC")
     (count 5669532))
   (<http://purl.org/vocab/resourcelist/schema#created>  5037)
   (<http://purl.org/vocab/resourcelist/schema#uri>  21071)
   (<http://lists.talis.com/schema/appConfig#feedbackFunction>  1)
   (<http://purl.org/dc/terms/created>  144982)
....

Thus I would assume my TDB dataset has the correct data in it... Perhaps my 
manifest file is not correct?


I don't think that is the problem.

Paolo


Thanks,

Chris

Re: Named graphs Fuseki/TDB

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