[Obscure Rule] applies for this entire chapter.
In SQL, a <reference type> is a pointer: a scalar constructed SQL <data type>.
It points to a row of a Base table that has the with REF
value property — that is, a <reference type> points
to a UDT value. Unless you are familiar with Object-Oriented Programming, this
chapter will probably not be fully comprehensible until you have read Chapter
27 "User-Defined Types".
