In Notes, a folder is implemented as a view, with the only difference being that a view has a selection formula that describes which documents should be in the view. A folder doesn't. From the point of view of a document, these two are quite different. It's easy to see if a document is in a view or not by executing the view selection formula against the document. A folder works by maintaining a list of documents that it contains. Documents themselves don't know which folders they are in.

This starts to cause a problem when you start playing about with database designs, particularly if you delete and recreate the Inbox folder in a mail database. If you delete the inbox folder, the list of documents that is in that folder vanishes with the folder. Create a new Inbox, and the new one is empty. There's a whole number of ways that this scenario plays out, but the bottom line is that the inbox is empty. And the owner of the mail file will be muttering dark threats at the Admin people whom he will be blaming for this.

Another version of this scenario is the one where people can't find where they have filed documents in their mail. They can see the document in All Documents -- which is a view -- but they can't find it in any folder, and the Notes mail database doesn't give them any help in finding which folder it is in. More dark mutterings are heard, calling into question the parentage of everyone involved in Notes from Ray Ozzie down to the most junior System Admin person.

Actually both of these scenarios are quite simple to solve. One of my customers has taken one of the solutions I'm about to offer to heart, and has added it as an action to his mail file template. Both solutions hinge around the LotusScript NotesDocument.FolderReferences property, which when properly enabled, allows you to see what folders a document is stored in.

To set this up you need first to copy two hidden views to the design of the database in question -- unless it's a mail database, in which case they are already there. These views are $FolderInfo and $FolderRefInfo. You can copy them from a Notes mail template from any of R5, ND6 or ND6.5 into your target database. Once you've done that, you need to turn on FolderReferences, which seems to be the point where these views are populated.