* molgenis_rdf_test :
   * delete  digital_identity_table . (Problem with xref)
   * Clear also in files : db_ui.xml , db_db.xml
   * still problem with som reference in
     * de.fuberlin.wiwiss.d2rq.D2RQException: Column @@digital_identity.digital_identity_id@@ not found in database (E0)
     * This reference is in the mapping file . recreate mapping file ! or just delete table from mapping :
       * * $$$ d2r-server -p 2020 molgenis2.n3
       * http://localhost:2020/snorql/ working
       * mapping in file
         * /Users/despoina/Documents/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp2/wtpwebapps/molgenis_distro/WEB-INF/
         * also changed.
 * Links
   * http://www.w3.org/2007/03/RdfRDB/papers/d2rq-positionpaper/ *
   * http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.0010057  !!