An extended relational algebra for nested relations

In this study the database models of Roth-Korth-Silberschatz (RKS) [cf. ACM TODS 13(4): 389—417, 1988] and Abiteboul-Bidoit (AB) [cf. Journal of Computer and System Sciences 33(4): 361—393, 1986] to formalize non-firstnormal-form relations are presented along with their extended relational algebra. We show that the extended set operators union and difference of RKS and AB are not information equivalent Using the model of RKS and restricting ourselves to union and difference, we define our extended set operators and show that these two operators and the extended intersection of RKS are information equivalent.