The Derivatives Archive or repository, is used to archive the derivatives (new versions) of original images contained in the master archive. Using this second archive enables both to grow independently over time. This was a design decision as in practice most image will start in the master repository only the best will be selected for further use most of which will be edited in some way. Having the Two archives allows archiving to archive media such as Blu-Ray disks much easier as the likely hood of updating previously archive images less likely.
The reason for this is, as new original images are added then new dated folders will be added with around the current date, images taken a year ago will hopefully already be in the archive and will have be archived to permanent media. So only resent folders will be in a state of flux. Derivative images (new edited versions of originals) may be taken from anywhere in the archive, but the new edited versions will be stored under the date that they where added to the derivatives Archive not the original date of the original master images, as they are new images that are derived from the original, or new images derived from earlier versions of the original. So in this case it is even less likely that previous folders will be added too. Thus the need to re-archive to permanent media less likely.
Versioning in the Derivatives Archive
In the masters Archive there is only one version, the master. In the derivatives Archive however the may be many versions. Each new version of an images will carry information as to the image it was derived and its file name will be the original file name with the date that the original was taken. This will then make the file name unique in the Derivatives Archive. To make the file name unique within versions the version number will also be added so for example an original image file name may be DSC01237.jpg will become 20170116-DSC01237[001].jpg in the Derivatives Archive.
Metadata
As each version is derived from the master image then this will contain the bulk of the images metadata such as where the image was taken the camera etc. The derived version only needs to contain a comment as to why to was edited, by who, the date edited, possibly the image editor etc, along with the details of the original and if applicable the previous version it was derived.
Metadata associated with each image version
The unique sequence number.
The Original file name