package MyDBClass;

use MyCalendar;

sub new {
   my $class = shift;

   ...
   my $self = ...;
   ...
   $self->{'_calendar'} = MyCalendar->new();
   ...
   return bless $self, $class;
}

sub Calendar {
   return $self->{'_calendar'};
}

...

##</code><code>##

   my $db = MyDBClass->new();

   $db->Calendar()->CalendarFunction(...);