[Digikam-users] Digikam XMP schema ?

[Jean-François Rabasse]

Hello Marie-Noëlle,

On Sun, 17 Feb 2013, Marie-Noëlle Augendre wrote:

> Could this ordered/unordered thing be related to the fact that tags are a
> complete mess (in fact, I don't manage tags anymore, waiting for a solution
> for that problem) when one tries to reorganize the tags hierarchy?

Not at all. This distinction has no technical implications, it's only a
matter of semantics when using metadata values.
Metadata properties may be of simple type, one name + one value, or list
type, one name + one or more values. And in the XMP standard, lists are
implemented exactly the same way. It's us to users and applications to
consider the values as unordered (a « bag » in RDF terminology), or to
consider ordered values (a « seq » in RDF terminology) with the 1st value
being more important than the second, the second value more important
than the third, etc.

And managing ordered lists from within an application would imply the
application interface offers a way to indicate how a newly added value
should be sorted among existing values, « add this in first place, or at
the end, etc. » And this is not what seems to be done with DK tagslists.

As for me, if I have two tags on an image, one to indicate the place,
e.g. Location/France/Paris, and one to indicate an image context,
e.g. Context/Urban/Street Art, I don't see reasons - for me - to say
the first tag is more/less important than the second.

As for the reorganisation problems you point out, my opinion is that it
comes from the way DK writes/read back tags between the images and the
database. When writing, all tags associated to the image (in the 
database) are written. When reading, all tags found in the image are
added to the associated tags in the database. But existing tags (in DB)
are kept even if they no longer are in the image.
The process isn't symmetric, and that's why reorganisation is painful.

Probably the good approach is to reorganize from outside Digikam, with
some metadata edition tools, then delete all tags in Digikam and
re-read metadata from all images. This guarantees the DB will reflect
the images content.

Regards,
Jean-François