How to find a package containing a given executable

["Moore, Paul" <Paul.Moore@uk.origin-it.com>]

Hi,
One of the most common queries I have with the Debian packaging system,
which I don't know how to make, is to search for the name of the package(s)
which install a given file or files. For instance, the most recent such case
I have was looking for the gvim executable. As it happens, this is provided
by vim-gtk, but that isn't obvious.

Clearly, on an installed file, I can use dpkg -S, but what about looking for
where I install something from?

If there isn't a simple tool to do this (or even if there is!) is there a
more structured or navigable list of what packages do what in Debian (no,
dselect doesn't qualify, IMHO)?

Paul.