Rewriting nested XML queries using nested views

Abstract

We present and analyze an algorithm for equivalent rewriting of XQuery queries using XQuery views, which is complete for a large class of XQueries featuring nested FLWR blocks, XML construction and join equalities by value and identity. These features pose significant challenges which lead to fundamental extension of prior work on the problems of rewriting conjunctive and tree pattern queries. Our solution exploits the Nested XML Tableaux (NEXT) notation which enables a logical foundation for specifying XQuery semantics. We present a tool which inputs XQuery queries and views and outputs an XQuery rewriting, thus being usable on top of any of the existing XQuery processing engines. Our experimental evaluation shows that the tool scales well for large numbers of views and complex queries.

Optimizing XML queries: Bitmapped materialized views vs. indexes

“…A number of papers have recently addressed the important problems of XML query rewriting using views and of XML view selection for materialization [41,9,42,43,11,10,44,13,45,46,14]. A common assumption made by most of these works is that a view materialization is a set of subtrees rooted at the images of the view output nodes, or references to the base XML tree.…”

“…The paper also studied a view selection problem defined as finding a minimal view set that can answer a given query. In [42,44] the equivalent rewriting problem has been addresses but for queries and views which are XQuery expressions. Elghandour et al [51] addressed the problem of selecting relational materialized views for XQuery queries.…”

Materialized view selection for XQuery workloads

“…A second important difference is that [11] and [19] assume that each query can only be re-written based on at most one view, while we (as well as e.g., in [14,17,27]) consider query rewritings based on multiple views. This significantly complicates our setting, since for each query q and n candidate views, up to 2 n view sets may be used to rewrite q, instead of just n. Also, as our experiments will show, the algorithms [11,19] by design do not capture the opportunities of multiple view-based rewritings, and in our setting, different algorithms exploiting these opportunities can achieve much better savings.…”

“…In contrast, we focus on materialized views that can help to completely answer complex queries, featuring multiple returning nodes and value joins. In the space of XML view-based query rewriting, closest to our work are the equivalent rewriting algorithms: for an XPath query using one view [11,12,13,31], and for XPath/XQuery using several views [14,15,16,17,20,21,27,32]. In this work, we built a view selection framework that exploits the recent multiple-view equivalent rewriting algorithm of [16], capable of handling tree patterns with multiple return nodes and value joins.…”

Parameterized XPath Views

“…[11,23] focus on subsets of XPath for polynomial time algorithms. [16] covers query rewriting using XQuery based views. In our approach we focus on a query rewriting to find an identical match (cf.…”