Well get rid of the today table thats a waste of time that can be done through queries, Im guessing the purchases tables is company purchase? if so you probably wanna make this more clear Stock_Purchase or summin simple like that. Consistency is not good stick with your names i.e. I see Catergory_ID and Catergory related make sure they are one or the other... read up on your normalisation... Date_Begin & Date_End for suppliers? whats that? Unless its stating some sort of term of contract you dont need it all supplier transaction dates should be held within the purchases table!
read up on normalisation cant stress that enough for you.
be paitent with people & they will respond this is a free, friendly environment not a ***** house of geekdom where your the pimp-daddy....
read normalisation! did i say that already? lol