Query translation from XPath to SQL in the presence of recursive DTDs
We study the problem of evaluating xp ath queries over xml data that is stored in an rdbms via schema-based shredding. The interaction between recursion (descendants-axis) in xp ath queries and recursion in dtd s makes it challenging to answer xp ath queries using rdbms . We present a new approach t...
Saved in:
Published in | The VLDB journal Vol. 18; no. 4; pp. 857 - 883 |
---|---|
Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
Berlin/Heidelberg
Springer-Verlag
01.08.2009
Springer |
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | We study the problem of evaluating
xp
ath queries over
xml
data that is stored in an
rdbms
via schema-based shredding. The interaction between recursion (descendants-axis) in
xp
ath queries and recursion in
dtd
s makes it challenging to answer
xp
ath queries using
rdbms
. We present a new approach to translating
xp
ath queries into
sql
queries based on a notion of
extended
XP
ath expressions
and a simple least fixpoint (
lfp
) operator. Extended
xp
ath expressions are a mild extension of
xp
ath, and the
lfp
operator takes a single input relation and is already supported by most commercial
rdbms
. We show that extended
xp
ath expressions are capable of capturing both
dtd
recursion and
xp
ath queries in a uniform framework. Furthermore, they can be translated into an equivalent sequence of
sql
queries with the
lfp
operator. We present algorithms for rewriting
xp
ath queries over a (possibly recursive)
dtd
into extended
xp
ath expressions and for translating extended
xp
ath expressions to
sql
queries, as well as optimization techniques. The novelty of our approach consists in its capability to answer a large class of
xp
ath queries by means of only low-end
rdbms
features already available in most
rdbms
, as well as its flexibility to accommodate existing relational query optimization techniques. In addition, these translation algorithms provide a solution to query answering for certain (possibly recursive)
xml
views of
xml
data. Our experimental results verify the effectiveness of our techniques. |
---|---|
ISSN: | 1066-8888 0949-877X |
DOI: | 10.1007/s00778-008-0131-0 |