It seems that nepomuk-core in rawhide needs version 6.1.6 [1,2]. Rawhide
currently provides virtuoso-opensource-6.1.7-1.fc20.
For now I downgraded virtuoso-opensource to virtuoso-
opensource-6.1.6-3.fc19.x86_64 and everything looks fine.
Do I have to open a bugreport for this? nepomuk-core or virtuoso-opensource?
 .xsession-errors: nepomukstorage(1236)/nepomuk (storage service):
NepomukStorage only works with virtuoso 6.1.6