IdentityInterface.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Framework\DataObject;

/**
 * Interface for
 * 1. models which require cache refresh when it is created/updated/deleted
 * 2. blocks which render this information to front-end
 */
interface IdentityInterface
{
    /**
     * Return unique ID(s) for each object in system
     *
     * @return string[]
     */
    public function getIdentities();
}