Does all this actually work already?

interpretation of τ expressions

my $tm  = new TM ('mymap.xtm');             # reading from file

my $dns = new TM ('dns:mydns.example.org'); # virtual map

use TM::Virtual::DNS;
$TM::schemes{'^dns:'} = 'TM::Virtual::DNS'; # setting up a...
$dns    = new TM ('dns:mydns.example.org'); # custom virtualizer

# federating maps
my $fed = new TM (tau => 'file:mymap.xtm + dns:mydns.example.org');

my $q   = new TM ('myquery.atm');           # reading in a query
my $r   = $fed->apply ($q);                 # apply it

my $res = new TM (tau => 'file:myquery.atm * dns:mydns.example.org');

virtualizing SQL: only highly simplistic queries