this is about the database related to Accounts in 5th chapter. author has given a diagram in pg. no 143(vb.net edition) with all the constraints(primary key & foreign key) specified.

But, when i refer to the downloaded database diagram in sql enterprise manager, i don't find any contraints except primary key on
userid on accounts_users table.

what could be the possible explanation for this aberration

help appreciated

I believe that is in the Errata on the book's actual page on this site (under browse books). There is an error on the diagram on page 143.