gistfile1.php

<?php
// $Id$

/**
 * Implement hook_schema().
 */
function relation_schema() {

  $schema['relation_allowed'] = array(
    'description' => 'Table for storing permitted relations between content types',
    'fields' => array(
      'id' => array(
        'type' => 'int',
        'description' => 'Autoincrement ID',
        'unsigned' = TRUE,
        'serial' = TRUE,
      ),
      'node_type_left' => array(
        'type' => 'int',
        'description' => 'The lefthand content type',
        'unsigned' => TRUE,
        'not null' => TRUE,        
      ),
      'node_type_right' => array(
        'type' => 'int',
        'description' => 'The righthand content type',
        'unsigned' => TRUE,
        'not null' => TRUE,        
      ),