For example:
$ms[0] = \%m1 ( a => 'x1', b => 'y', c => 'z1' );
$ms[1] = \%m2 ( a => 'x2', b => 'y1', c => 'z2' );
$ms[2] = \%m3 ( a => 'x3', b => 'y', c => 'z3' );
$ms[3] = \%m4 ( a => 'x4', b => 'y2', c => 'z4' );