BibTeX entries exported from online databases such as IEEExplore have keyword fields containing information that was decided by the authors or editors. However, I want to define my own non-hierarchical classification (i.e., tags or custom keywords) to use in my BibTeX database, without clearing the original keywords field.
What BibTeX field should I use for such classifications? Ideally, I'd like to be able to add tags and query entries of my tags with a tool such as JabRef. There's a video that explains tagging in Mendeley, but I'd like to achieve the same with some BibTeX software.