nie:license and nie:copyright have common single-valued superproperties
tracker-miners#20 (comment 299337) mentions this line of log:
Could not insert metadata for item "file:///home/../hear-our-voices-summary-report-english.pdf": Unable to insert multiple values for subject `urn:uuid:8f866e62-5d67-a8ef-55c0-26cfc7e1fa0f' and single valued property `dc:rights' (old_value: 'Copyright 2014, Plan International. Licensed to the public under Creative Commons BY-NC-ND 3.0.', new value: 'http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en_GB')
This is an intesting one, the PDF extractor does nothing directly related to dc:rights. After some investigation about how could this happen, the PDF extractor however does possibly set both nie:license and nie:copyright. These make sense as separate high level entities, but they both are defined in the ontology as subproperties of the same single-valued parent properties. The Hierarchy is:
dc:rights \- nie:legal |- nie:license \- nie:copyright
Due to Tracker obeying RDFS entailment, setting either of those 2 properties will result on dc:rights and nie:legal being set in addition, so there may be conflicts on these 2 properties if nie:license and nie:copyright contain different strings.
This is an ontology bug. Checking the latest instance of NIE ontology (In wayback machine, sigh...), none of these properties have cardinality restrictions. We should do the same here.