My book gives the IUPAC name of $\ce{KAl(SO4)2.12H2O}$ which is nothing but emperical formula of potash alum as
"Potassium aluminium (III) sulphate -12 water"
But Wikipedia gives it as "Aluminium potassium sulfate dodecahydrate" , though there could be change in name because of number of water molecules but there is significant difference between the two names
So, my question is how to give IUPAC name to a double salt (potash alum is a double salt), and why is there difference between two iupac names I.e the one which is given in my book and the one in wikipidea.