Add documentation that explains semantics of core namespace fields #28
Description
Muninn itself assumes specific semantics for some of the fields of the core namespace (or linked to the availability/unavailability of such fields).
For instance:
- product_type requiring a link to a muninn plugin
- active (is set to false while files are being copied into the archive; should not be used to manually set entries to a 'disabled'/'deleted' state; entries that have active==false and are not in an ingest/pull state means that an error occurred during ingest/pull)
- archive_date/archive_path (only set when there is a local file in the archive)
- archive_date is the date at which the product was put in the muninn archive (archive dates of other archives should be stored using separate namespaces)
- difference between physical_name and product_name
- remote_url and muninn-pull link
- footprint (and use of geography type for postgresql)
- automatic update of metadata_date
We need to add information on this to the muninn documentation.
We also need to clarify which entries are automatically set by muninn and which can/should be set using plugins (or via create_properties).