The relational model with relation-valued attributes

摘要

Motivated by new applications of database systems we introduce relations which may have relation-valued attributes and propose a related algebra. Formal definitions for this extended relational model can be given by applying usual notions recursively. The main problem considered in this paper is the formal definition of an appropriate relational algebra for these non-first-normal-form relations. We allow the application of the basic relational operators to any relation-valued attribute within a relation. This leads to a (hierarchically) nested relational algebra.