How is density of a substance in grams per cubic centimeter a discrete attribute? I'm going over the different types of attributes in data-mining (nominal, ordinal, discrete, etc) and there is one example in the book that states that the density of a substance in grams per cubic centimeter is a discrete attribute. Why is this? I confuses me that this is the case but it also says that the distance from the center of campus is continuous.
The book is wrong.  Density is continuous.  It could be any real number.  You are quite right.