Linked Open Data Extension on the RapidMiner Server

[Patrick Westphal]

Dear RMLOD developers,

I tried to use the Linked Open Data Extension on the RapidMiner Server
(7.2) but got an error I don't really understand.

To reproduce this error a simple process setup would be to just get the
RDF properties of an OWL file (XML description attached). As data
connection I'm using the OWL file available at [0]. The XML snippet
defining its settings is also attached. Running this process in the
RapidMiner Studio (7.1) I get the expected results. However, triggering
the execution of the same process remotely on a RapidMiner Server I get
back nothing. On the server side I see a NullPointerException and the
quite general message 'Problem in SPARQL Based Linker'. (The whole trace
is attached as well.) The RapidMiner Studio and the RapidMiner Server
run on the same machine so there shouldn't be an issue with the file path.

Since there seems to be no source code of the Linked Open Data Extension
available I cannot further debug this problem. I saw that there was a
compatibility statement in the operator description
(compatibility="7.1.001") and I wanted to test the same setup on an
older version of the RapidMiner Server, but unfortunately I was always
guided to the latest version for download. So, do you think this is a
compatibility issue and it's currently just not possible to use the
Linked Open Data Extension on a 7.2 RapidMiner Server or is there a
problem somewhere else?

Thanks in advance,
Patrick

[0]
https://github.com/AKSW/SML-Bench/blob/develop/learningtasks/carcinogenesis/owl/data/carcinogenesis.owl

--
Patrick Westphal
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Phone: +49-341-9732305

[Petar Ristoski]

Hi Patrick,

I apologize for the late response, I was on holidays.

I didn't import the process in RapidMiner server, but based on the exceptions you got in trace.txt, it looks like you haven't defined the "carcinogenesis" SPARQL connection in the RapidMiner server. You need to create the SPARQL connection from "Administration -> Connections -> Add Connection". Did you do that already?

Cheers,

Petar

[Patrick Westphal]

Hi Petar,

thanks for your reply. Yes, I created the connection first (and it was
listed in the connections overview in the server's web ui). But I
created it via a SOAP and it seems I either forgot to define a field
(use_count) or messed up a file path. Anyway, it is fixed now and wasn't
really an issue on the LOD Extension side. So everything is working
fine, now.

Thanks and best regards,
Patrick