Difference between GL account type and class

[Jacopo Cappellato]

What is the difference between the the type (glAccountTypeId) and the 
class (glAccountClassId) of a GL account (GlAccount)?

In the Data Model Resource Book there is no mention of classes but my 
guess is that the information that we store in the class is the same 
that in the Book is stored in the type field... am I wrong?

Thanks,

Jacopo