magento: fetching MPN( manufacturer part no ) or UPC (Universal product code)

I tried searching for MPN and UPC in the magento 1.4 - 1.5 database. Seems they're non existent or may be named differently. In which table can i find these values? i tried this

Mage::app();
$pr开发者_如何学JAVAoducts = Mage::getModel('catalog/product')->getCollection();
$products->addAttributeToSelect('*');
$products->load(); 

    <mpn><![CDATA['. $product['mpn'] .']]></mpn>

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Magento comes stock with SKU (your in-store part number) defined.

For adding UPC or manufacturer part numbers, you will need take advantage of Magento's "out of the box" extensibility and add these as custom product attributes.