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Unlike a collection there is no data schema for Independent Media Items. You can add custom data fields using the Media Item Editor, but there is no Record Editor with the IMI since there are no records.
If you're not sure how to structure a collection but want to add your content to the system, uploading to the IMI is a good idea. You can then organize the content using labels and easily copy items into a collection. Once a media item is copied into a collection a blank record is created for you. The IMI allows you to add the same item to different collections. Consider it as a staging area for the content you haven't organized or cataloged yet.