A question by C. J. Date in point #1 on page 81 chapter 5 "Relational Algebra" of the 2005 book : "Database In Depth - Relational Theory for Practitioners" has caught my attention. I quote:
"First, the operators are generic; they apply, in effect, to all possible relations. For example, we don't need one specific join operator to join employees and departments and another, different join operator to join suppliers and shipments. (Incidentally, do you think ano analogous observation applies to object-oriented systems?)"
I would like to comment on this shortly
