In the first versions of MArcomage card related data were stored in relational DB. Of course both relational DB and XML DB have pros and cons. Then u-mage came with an idea to transfer all persistent data (data that would not be changed by user) to XML files. Sure, they are slower, but acceptable for our purposes. The development of cards has much improved since then. Before, the card effect code was stored separately from the rest of the card data. Now, all card related data is stored in one place and also all keyword related data as well.
The diffs are much easier to read and consistency between card effect text and card effect code are more easier verified. I think this change was a vast improvement. Not to mention that this change reduced the parsing time of card effect.