@Charles - with regards to your other post. Surely one of the major issues that was mentioned earlier by theDucks is that Authors are not treated as a separate known entity in the Calibre database. i.e. they are derived from books that happen to share a name.
So a link "column" won't make practical sense unless it is associated with the "Author" as you wouldn't want to have to store it at per book level for each of the books.
And as theDucks points out, you have the issue of authors disappearing when books are removed, renaming of authors merging them etc.
Others mentioning a separate database I think would cause more problems than it would be worth imho - all the issues of moving libraries, upgrading, backups etc meaning something else that has to be taken into consideration. If such a feature were to exist I think it has to be inside the Calibre database to be practical.
I don't think it is a trivial problem to solve - that is not to say that for the benefit of the long term in Calibre it could/should not be tackled at some point. I know I have expressed no interesting in writing a plugin to attempt to manage it in the past. However that is not to say I would not use such a feature if it already existed in Calibre.
