/usr/lib/swi-prolog/library/semweb/ is in swi-prolog-nox 6.6.4-2ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/swi-prolog/library/semweb/INDEX.pl
/usr/lib/swi-prolog/library/semweb/README
/usr/lib/swi-prolog/library/semweb/dc.rdfs
/usr/lib/swi-prolog/library/semweb/eor.rdfs
/usr/lib/swi-prolog/library/semweb/owl.owl
/usr/lib/swi-prolog/library/semweb/rdf_cache.pl
/usr/lib/swi-prolog/library/semweb/rdf_compare.pl
/usr/lib/swi-prolog/library/semweb/rdf_db.pl
/usr/lib/swi-prolog/library/semweb/rdf_edit.pl
/usr/lib/swi-prolog/library/semweb/rdf_http_plugin.pl
/usr/lib/swi-prolog/library/semweb/rdf_library.pl
/usr/lib/swi-prolog/library/semweb/rdf_library.ttl
/usr/lib/swi-prolog/library/semweb/rdf_litindex.pl
/usr/lib/swi-prolog/library/semweb/rdf_ntriples.pl
/usr/lib/swi-prolog/library/semweb/rdf_persistency.pl
/usr/lib/swi-prolog/library/semweb/rdf_portray.pl
/usr/lib/swi-prolog/library/semweb/rdf_turtle.pl
/usr/lib/swi-prolog/library/semweb/rdf_turtle_write.pl
/usr/lib/swi-prolog/library/semweb/rdf_zlib_plugin.pl
/usr/lib/swi-prolog/library/semweb/rdfs.pl
/usr/lib/swi-prolog/library/semweb/rdfs.rdfs
/usr/lib/swi-prolog/library/semweb/sparql_client.pl
/usr/lib/swi-prolog/library/semweb/turtle.pl