Generic file finder question ..what tool or database

[Harry Putnam <reader@newsguy.com>]

If I have the name of a file like xpm.h and want to know what package
contains it.  And I find that `apt-cache search xpm.h' doesn't know
about it.

And dpkg -S xpm.h doesn't either

I'm assuming that means it isn't here but might be in a
package in the distro on line somewhere.

Where is the database with this kind of information? 
search.debian.org isn't the right place I don't think

One can compile a (rough) list of all file names in the install with:
Something like:
dpkg -L $(dpkg -l|awk '{gsub(/^..../,"",$0);print $1}')

And with a little script, print the package name on each line too.

But where is a database that contains that kind of information for all
packages in a distribution? That is, a list of all the file names in
all the packages of a distribution.