On Roth, Korth, and Silberschatz's extended algebra and calculus for nested relational databases
Abdullah Uz Tansel, Lucy Garnett · ACM Transactions on Database Systems · 1992
We discuss the issues encountered in the extended algebra and calculus languages for nested relations defined by Roth, Korth, and Silberschatz.[4]. Their equivalence proof between algebra and calculus fails because of the keying problems and the use of extended set operations. Extended set operations also have unintended side effects. Furthermore, their calculus seems to allow the generation of power sets, thus making it more powerful than their algebra.