Please add a possibility to find images NOT containing keywords, tags etc.
Just for illustration: Lightroom’s approach
Note: Lr has two dropdowns. The first sets the kind of data to search, the second (expanded) dropdown sets the condition. The shown selection and highlighted item correspond to “search images without keywords” Note that “Ohne” (without) is used if a specific keyword should be absent. Better wording: “Enthält nicht” (does not contain).
I support that request but am afraid that this will only be possible within a folder, not over all images in a folder structure. Creating a project with “all pictures” will not help as searching within projects is not possible.
I just ask how practical is such a search in face of all DAM shortcomings of PL? So once again, something for the apparently necessary DAM software aside from PL.
Currently research is done on the whole catalog?
I think the search for the absence of keywords is the same, only the chain of character changes, “null” in this case.
You mean the search in the search field above the folder tree? I forgot that this exists, I used the filter options and they are (of course) limited to the folder currently selected.
Keywords are stored in the catalog (database) in the table ZDOPKEYWORD
The relation between the images and keywords are stored in Z_10KEYWORDS
When I now switch to the table ZDOPITEM, I’ll find the names of the respective files and DPL will be able to find the file(s) with the built-in search function.
If you’re fluent in SQL, you could write a query that lists the files not linked keywords etc. Quite tedious, isn’t it. Much easier if DxO added the respective search or smart project.
That’s so much easier and more convenient than in LR (take that, Adobe…) 
Wow @platypus you’re walking in galaxies beyond my horizon. 
I have just done the same for Windows, in the database there are tables:
Yes, if “Itemid” is not in the ItemsKeyword table, it doesn’t have a keyword.
…that’s the thing with galaxies, they usually are. 
On the other hand, databases are just lists of items and relations, nevertheless, exiftool finds those files with less effort…
Some library’s have a tool called “lost and found”.
First you need to checkbox all folders which are open for the library and (exclude the not for this library suitable/needed)
And then you should be able to find the orphans(XMP’s and Dopfiles without a imagefile) and not tagged imagefiles.
like a search engine for:
1 “unprocessed” which we have but only folder for folder not globally. (i like to find all not processed images in my stacked folders.)
2 orphans like only XMP’s no image (deleted images which are cut from xmp and dopfiles)
3 non tagged images and prefable with a sub selection as in [keywords], [GPS], [IPTC content]