On Relational Support for XML Publishing: Beyond Sorting and Tagging

SIGMOD |

Published by Association for Computing Machinery, Inc.

In this paper, we study whether the need for e cient XML
publishing brings any new requirements for relational query
engines, or if sorting query results in the relational engine
and tagging them in middleware is su cient. We observe
that the mismatch between the XML data model and the
relational model requires relational engines to be enhanced
for e ciency. Speci cally, they need to support relation-
valued variables. We discuss how such support can be pro-
vided through the addition of an operator, GApply, with
minimal extensions to existing relational engines. We dis-
cuss how the operator may be exposed in SQL syntax and
provide a comprehensive study of optimization rules that
govern this operator. We report the results of a prelimi-
nary performance evaluation showing the speedup obtained
through our approach and the e ectiveness of our optimiza-
tion rules.