Hi,
some databases (EF 3.1 db) use the data quality of the whole process. Hence, this field is filled if a process DQ is chosen with the respective entries. There is not numerical uncertainty attributed to it. Still, in openLCA you will see DQ of the results per process but not per flow (if there is no DQ for the flow set). Normally in LCA databases there is either DQ for flows or for the process.
Hope this helps