Feature request related to this topic: Forum-Post (https://www.photools.com/community/index.php?topic=2673)
In some circumstances it could be helpful when data-driven categories are not build over the whole database but just over a subset. So I think in the panel "Edit Data-driven Category" there should be an additional field (new line) where you can configure a "Formula". In this case one can define a formula and the data-driven category is just build over the result of this formula.
Example: Building a data-driven category with Camera Make/Model not over the whole database but just over bookmarked images (or another collection, or a folder, or a category, or...)
+1 from me.
Here, data driven categories slow down imatch (although being on SSD), so maybe reducing them on subsets may make things faster.