On the Expressive Power of Node Construction in XQuery

Abstract

the relational model it has been shown that the rela- tional algebra has the same expressive power as the nested relational algebra, as far as queries over relations and with results are concerned (6). Hence, for each query that uses the nested relational model and that, with a table as input always has a table as output, there exists an equivalent query that only uses the relational model. In analogy, we study a related flat-flat problem for XQuery: for each expression containing operations that con- struct new nodes and whose XML result contains only orig- inal nodes, there exists an equivalent flat expression in XQuery that does not construct new nodes.