Apologies. Let's try without attachments!
As a picture is worth a thousand words, I built a mockup based on the
GIMP metadata editor. The Exif tab has been left alone as a lot of
that data comes straight from the camera. The XMP and IPTC tabs have
been merged and separated into tabs called: Who, What, Where, When
according to Metadata Working Group guidelines.
Under the hood, gexiv2 composite functions would be used to read and
write to the correct metadata fields.
Results can be seen on the following links:
gimp-developer-list mailing list
List address: email@example.com
List membership: https://mail.gnome.org/mailman/listinfo/gimp-developer-list
List archives: https://mail.gnome.org/archives/gimp-developer-list