Nomenclature in taxonomy

[Nicholas_Bokulich]

Hi @blues!

• "Unidentified" is a label that would come from the database, so indicates that that sequence is not annotated by that database, not an issue with the classifier.
• "Unclassified" indicates that the classifier could not classify the sequence at even kingdom/domain level... see the taxonomy topics here for details: Frequent Questions and "Best of the QIIME 2 Forum"

The meaning of other "empty" labels is here:

ASV collaps question

@shinseung, Those two labels are distinct: The first indicates that the sequence could not be classified beyond kingdom level (which probably indicates that it is really non-bacterial, e.g., host DNA). The second consists entirely of labels from the reference database you used. So QIIME is able to classify that sequence to the genus (or species?) level, but unfortunately the top match is to reference sequence(s) that are totally unannotated in the database. I hope that clarifies!