magento2/app/code/Magento/Sales/Model/Config/SchemaLocator.php

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

/**
 * Cron locator
 */
namespace Magento\Sales\Model\Config;

use Magento\Framework\Module\Dir;

class SchemaLocator implements \Magento\Framework\Config\SchemaLocatorInterface
{
    /**
     * Path to corresponding XSD file with validation rules for merged config
     *
     * @var string
     */
    protected $_schema;

    /**
     * Path to corresponding XSD file with validation rules for separate config files
     *
     * @var string
     */
    protected $_perFileSchema;

    /**
     * @param \Magento\Framework\Module\Dir\Reader $moduleReader
     */
    public function __construct(\Magento\Framework\Module\Dir\Reader $moduleReader)
    {
        $this->_schema = $moduleReader->getModuleDir(Dir::MODULE_ETC_DIR, 'Magento_Sales') . '/' . 'sales.xsd';
    }

    /**
     * Get path to merged config schema
     *
     * @return string|null
     */
    public function getSchema()
    {
        return $this->_schema;
    }

    /**
     * Get path to pre file validation schema
     *
     * @return string|null
     */
    public function getPerFileSchema()
    {
        return $this->_perFileSchema;
    }
}