public static function getInstance()
 {
     if (!self::$dm) {
         self::$dm = new self();
     }
     return self::$dm;
 }
<?php

include_once "../database/lingerie-database-manager.php";
include_once "apriori-association-keyword-recommender.php";
$dm = LingerieDatabaseManager::getInstance();
$recommender = new AprioriAssociationKeywordRecommender($dm);
$recommender->preprocess();