protected function initializeProductRelation(array $attr)
    {

        // laod child/parent ID
        $childId = $attr[MemberNames::CHILD_ID];
        $parentId = $attr[MemberNames::PARENT_ID];

        // query whether or not the product relation already exists
        if ($this->loadProductRelation($parentId, $childId)) {
            return;
        }

        // simply return the attributes
        return $attr;
    }