XQuery_Rewrite_Optimization_in_IBM_DB2_pureXML.pdf

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XQueryRewriteOptimizationinIBMDB2

pureXML

Article·January2008

Source:DBLP

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XQuery Rewrite Optimization in IBM



DB2

∗

pureXML

Fatma

Ozcan

IBM Almaden Research Center

650 Harry Road, San Jose

Normen Seemann

IBM Silicon Valley Lab

555 Bailey Road, San Jose

Ling Wang

IBM Silicon Valley Lab

555 Bailey Road, San Jose

Abstract

In this paper, we describe XQuery compilation and rewrite optimization in DB2 pureXML, a hybrid

relational and XML database management system. DB2 pureXML has been designed to scale to large

collections of XML data. In such a system, effective ﬁltering of XML documents and efﬁcient execution

of XML navigation are vital for high throughput. Hence the focus of rewrite optimization is to consoli-

date navigation constructs as much as possible and to pushdown comparison predicates and navigation

constructs into data access to enable index usage. In this paper, we describe the new rewrite transfor-

mations we have implemented speciﬁcally for XQuery and its navigational constructs. We also brieﬂy

discuss how some of the existing rewrite transformations developed for the SQL engine are extended and

adapted for XQuery.

1 Introduction

XML has emerged in the industry as the predominant mechanism for representing and exchanging structured

and semi-structured information across the Internet, between applications, and within an intranet. Key beneﬁts

of XML are its vendor and platform independence and its high ﬂexibility. With the proliferation of XML data,

several XML management systems [7, 10, 17, 5, 4, 6, 12, 11, 14] have been developed over the last couple of

years. All major database vendors have released XML extensions to their relational engines, in addition to many

native XML management systems. XQuery [18] and SQL/XML [9] are the two industry-standard languages

that are supported by these systems to query XML. Most of the current research now focuses on optimization of

XQuery and SQL/XML in these XML management systems.

In this paper, we describe XQuery rewrite optimization within the context of

DB2 pureXML

[4], which is a

hybrid relational and XML database engine that provides native XML storage, indexing, navigation and query

processing through both SQL/XML [9] and XQuery [18], using the XML data type introduced by SQL/XML.

DB2 pureXML

stores XML data in columns of relational tables, as instances of the XQuery data model [19]

in a structured type-annotated tree. By storing binary representation of type-annotated trees,

DB2 pureXML

avoids repeated parsing and validation of documents.

DB2 pureXML

[4] query evaluation run-time contains

three major components for XML query processing: (1) XML navigation engine, (2) XML index run-time and

(3) the XQuery function library. Additionally, several relational runtime operators have been extended to deal

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Bulletin of the IEEE Computer Society Technical Committee on Data Engineering

∗

DB2 pureXML is a a trademark or registered trademark of International Business Machines Corporation.