Although, in a technical sense, groups and tags may be the same kind of entity treated in different ways, from the user’s point of view groups and tags are very different (because DevonThink treats groups and tags in different ways, groups and tags behave differently)!
However, groups don’t store files.
DevonThink is very different from what you might think initially: the entries in a DevonThink database aren’t files, groups aren’t folders and replicants aren’t aliases.
The entries in DevonThink are references to files. The files themselves are (by default) stored in the .filesnoindex folder in the database (you can move them outside the database if you put their references in an indexed group but this is rather tricky – try it only when you know what you are doing).
It is the references that are organized into groups, not the files themselves! For that reason, it is important to make a clear distinction between what happens to the file and what happens to the reference.
-
When you move an entry you move the reference, not the file.
-
When you replicate an entry (that is a reference to a file) you create another reference to that file (not a reference to the original entry as when aliasing!).
-
When you delete an entry you delete the reference; when you delete the last reference to a file in the group hierarchy (that is: when you delete an entry that has no replicants), the file is deleted too.
-
When you duplicate an entry you duplicate the file to which it refers and create a reference to that duplicate in the group hierarchy of the database.
From the user’s view point, groups are collections of references: if you delete a group those references will be removed from your database (and if an entry in that group has no replicants the corresponding file will be removed too!).
Tags, on the other hand, are, from the user’s point of view, properties of documents: if you delete a tag, this tag will be removed from all the documents but nothing happens to their entries (references) in the hierarchy.
Replicants provide a way to refer to a file at more than one place in your group hierarchy.
Tags provide a way to characterize files in a manner that does not fit with your group hierarchy.
For example, my group hierarchy sorts my journal articles according to their topic. When I design a course (a course typically covers different topics, but does not use all the literature I have about each topic), I tag the literature I want to use with the tag for that course. In this way, I can use my group hierarchy and the see also function to decide which articles to use and quickly access the articles I selected by means of the tag without making any changes in my group hierarchy.