A RECURSIVE ALGEBRA FOR NESTED RELATIONS

The nested relational model provides a better representational model for complex objects than the (flat) relational model by allowing relations to have relation-valued attributes. A recursive algebra for nested relations that allows relations to be accessed and modified at all levels without always having to flatten them is presented in this paper. The operators of the classical nested relational algebra are extended with recursive definitions so that they can be applied not only to relations but also to subrelations of a relation. Queries are much more efficient and succinct when expressed in this algebra than in languages that require restructuring in order to access subrelations of relations. A sketch of a proof showing the equivalence of the expressive powers of the recursive algebra and the nested relational algebra is given. © 1990.