Shelf life expiry days

Hi,

In /SAPAPO/MATKEY, I can get the shelf life of a material, which is the total number of days a material is good to be used. With reference to what date is this number defined? creation date or goods receipt date etc....

If I have to get the number of days left out for the product, where can I get that data in APO? any specific tables that can be used???

Thanks.