Image types Common requirements
metadata values are not updated and the old values lost; instead, new metadata values are added while the previous values are retained.
NOTE 2 Another reason for implementing multiple metadata groups is that the contents of different
groups become available at significantly different times. It is important to be able to input each group into the catalog andor archive when the data becomes available, thus avoiding update of the larger set of
metadata and data. For example, the data that is common to many images is often available months before most of the corresponding images are collected. Moreover, multiple versions of the same metadata are
recorded for a single image largely because it becomes available at significantly different times e.g., separated by days.
b These multiple metadata groups shall be linked, and the links shall be automatically traversed, to provide the “virtual” appearance of a complete structure that is queried
and retrieved as if they were one structure. c The metadata for multiple images shall be able to be aggregated into image
collections.
NOTE 3 Such image collections can be used to aid user comprehension and data management. For
example, all the images collected over a single target for the purposes of some analysis could be referenced as one logical collection of images. Such an image collection may be formed based on the
location of the target, date range of collection, and analysis theme, etc. Such a collection may be formed manually and maintained by a particular user. Indeed, a hierarchy or net of collections could be formed,
with some images included in multiple collections.
d The metadata for multiple images shall not be required to be aggregated into image collections, for any purpose.
NOTE 4 Useful and defined image collections do not exist for many images.