What you're looking for are Shell Extensions or more precisely Shell Namespace Extensions.
Ah, I remember there was an article in The Delphi Magazine which included sourcecode for exactly that! Shell Namespace Extensions.
Maybe someone that still has the issues (or the USB stick with everything, mine is pushing up daisies) can look it up for us. ( Howardpc?, Detlev? )
Must be one of the higher numbered issues.
Note that if that database is a
single table it is possible to write a plain file driver for it without the shell using a record describing all fields and file of Record But a bit of a hack since it is undocumented in FPC, not in Delphi, where it is
somewhat documented.