Using the SPARQL adapter with a Strabon (Sesame) database

[Olivier Dalang]

Dear list,

I've been playing around with Ontowiki atop a Virtuoso database, but I hit a few blocking bugs of Virtuoso (for reference : [1][2])...

So I'd love to try Ontowiki with another geo-enabled triple store. In my case : Strabon, which seems to have a more solid implementation of (Geo-)SPARQL. Strabon is based on Sesame, so my question probably applies to any Sesame database as well.

I've setup the Strabon endpoint, which works well. Then, in Ontowiki's config.ini, I changed

store.backend = sparql

and 

store.sparql.serviceUrl = "http://mysite.com:8080/strabonendpoint/";

store.sparql.graphs[]   = "http://mysite.com/mygraph/"

(from the source, it seems the graphs aren't automatically retrieved yet)

But then, when I go to the Ontowiki homepage, I get a "no data received" error. The ontowiki.log file is empty, but the erfurt.log file is full of this line :

2014-12-10T16:50:31+01:00 INFO (6): System configuration model not found. Loading model ... 

This line is repeated around 15'000 times, so there's definitely something wrong there... It seems Erfurt's not able to create the Sysconf model, but I don't know why.

I tested the Strabon SPARQL endpoint from a php script (using curl), and update queries work well even without authentification since it's on the localhost (even if the Strabon endpoint runs on Tomcat on port :8080 while Ontowiki runs on apache).

Any idea on what could be wrong ?

Is it right that if the Strabon (Sesame) endpoint is SPARQL compliant, I should be able to use the sparql adapter directly ? (because on some other thread, there was the mention that one should subclass erfurt adapter interface to have Ontowiki work with other databases).

Thanks !

Olivier Dalang
---
Digital Humanities Lab (DHLAB) - http://dhlab.epfl.ch
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Tel. +41 21 693 02 46

[1] : Problems deleting typed triples : https://github.com/openlink/virtuoso-opensource/issues/247

[2] : Bugs with ST_Intersect : http://sourceforge.net/p/virtuoso/mailman/message/32998479/

[Michael Martin]

Hi Olivier,

Using the SPARQL backend is currently the one and only way to speak with a Strabon database.

Problematically is, that the OntoWiki Sparql backend is a read only backend, which means that the system configuration models can not been written into the store (see your error message).

I had a use case, wherein i had a similar problem and wrote the following extension:

https://github.com/AKSW/sparqlservices.ontowiki

If you only need read only access, you can use that extension using the configuration described in the readme.md of that repo. (take into account the Note section of the extension)

Possibly that fits your needs.

Please feel free to ask while having further questions. 

Best Michael

--------
Dr. Michael Martin, M.Sc.
Department of Computer Science, University of Leipzig
Augustusplatz 10, 
04109, Leipzig, Germany

Phone: +49 341 97 32322
Research Group: http://aksw.org/
Homepage: http://bis.informatik.uni-leipzig.de/MichaelMartin

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[Olivier Dalang]

Hi,

Thanks for your answer.

Is there a reason why the adapter is read only, or is it imaginable to extend it to support update queries as well ?

Best,

Olivier