I have been able to link from and entry in an RTF document in a data base to a sheet.
However, the back arrow in the sheet is not active, so I cannot go back to the RTF document navigating through the folder structure. I can assign a URL (for the RTF docunemt) to a record in a sheet, I think, but how do I write the URL for this. Or is there a way I can copy and paste the URL. Better yet, is there another way to create this link in an easier way. Thanks for any help! 
Jerry, sorry but at this time a link cannot be established from a sheet or record to another document in the database.
The linking techniques in DEVONthink work only from rich text documents, and sheets and records contain plain text.
So a link can be established from a rich text document to a record, but not from a record to another document.
Consideration is being given to a change in the future, but no promises at this time.
The next release will support this (actually it’s already working in document windows but not in main windows).