A method is needed to determine which goods within a store should be classified as Digital Goods. For some stores this may be all of their inventory, for others it may just be a subset.
Generally it would be expected that any ‘virtual’ product would be Digital Goods, however this may not always be the case. We may therefore need some extra ‘flag’ for digital goods.
There are further complications in that some EU countries have specific VAT rates for e-books, so these may need to be flagged separately. Although that flagging may simple be done by assigning a Tax Class to the product.
(See Determining Tax Rate)