xml databases

XML: What and Why? Application: Web Services XQuery: The XML Query Language Good News: XQuery, as a declarative

language, is ideal for automatic parallel execution

Bad News: We still need Java We limmit the “automatic parallel execution”

XQueryP scripting extension and the tradeoff

CS315B

<language type=”computer language”><name> XML </name><description> A universal format

for structured documents and

data. </description>

</language>

XML is designed to describe data and to focus on what data is.

HTML is designed to display data and to focus on how data looks.

Thus, HTML is about displaying information, while XML is about describing information.

CS315B – Domain-specific Languages for Parallelism CS315B – Domain-specific Languages for Parallelism

Can represent a wide variety of both structured and unstructured data

Can be used in integrating heterogeneous data sources (traditional/relational databases , data files, email messages, web pages, etc.)

Can be used on a variety if devices including PCs, PDAs, smart mobile phones, etc.

B U T M A I N L Y . . . ”Helps companies to cut costs in

information exchange”CS315B – Domain-specific Languages for Parallelism CS315B – Domain-specific Languages for Parallelism

Differences

Commonalities

XML Relational Data Model

Tree Table

Data and schemas should not be correlated.Data can exist with or without schema, or with multiple schemas.

Schema first, then data

XML

Logical and Physical Data Independence

Declarative Semantics


A WS is a class on the Web. Like an RPC, which identified by a URI (e.g.

http://my.service:234)accepts as argument an XML envelope returns an XML response.

Server Application Logic

Client

Web Service

XML

Client

XML

Client

XML


Typical Architecture

Server Application Logic (Java / .NET)

Web Service (XML Domain)

XML DB

XML

XQuery (XML Domain)


Client

Web Service

XML


XQuery is a declarative programming language, designed to manipulate and query XML data.

With XQuery you describe ’’what’’ you want to achieve and leave the ’’how’’ to the runtime system

It is essentially designed for optimizability, including automatic parallelization of the execution of the queries



<<bookbook> > <<ISBNISBN>> 333 333 <</ISBN/ISBN> > <<titletitle>> RDBMS RDBMS <</title/title>> <<authorauthor>> Paul Paul <</author/author>> <<chapterchapter>> <<numnum>> I I <</num/num>> <<titletitle>> Information Retrieval using RDBMS Information Retrieval using RDBMS <</title/title>> <<sectionsection>> <<titletitle>> Beyond Simple Information Retrieval Beyond Simple Information Retrieval <</title/title>> <<sectionsection>> <<titletitle>> Extension of RDBMS features Extension of RDBMS features <</title/title>> <</section/section>> <</section/section>> <</chapter/chapter>><</book/book>>

Syntactic sugar that combines FOR, LET, IF

Example Return the number of title elements of the chapter ”I” of the book

FOR var IN expr

LET var := expr WHERE expr

RETURN expr

XQUERY SQL Analogy

FOR $chapters IN /book//chapterLET $titles := $chapters//titleWHERE $chapters/num = ”I”RETURN <NumOfTitles> count($titles)

</NumOfTitles>

similar to FROMno analogy in SQLsimilar to WHEREsimilar to SELECT



((docIddocId, , sPossPos, , ePosePos, , levellevel))

docIddocId: identifier of the document: identifier of the documentsPossPos : starting position of the element or string within the XML doc: starting position of the element or string within the XML docePosePos : end position of the element (for string => same as sPos): end position of the element (for string => same as sPos)levellevel : nesting depth within the document: nesting depth within the document


To facilitate the evaluation of the XQuery expressions, an index is created for all the nodes within the XML database.

Term docId

sPos

ePos

level

book 1 1 36 0

ISBN 1 2 4 1

title 1 5 7 1

chapter

1 11 35 1

title 1 15 20 2

title 1 22 26 3

title 1 28 32 4

RDBMS

1 6 6 2

RDBMS

1 19 19 3

RDBMS

1 30 30 3

”Beowulf cluster”: An example of a high performance parallel computing system used for parallel processing of XML Queries

Several processing nodes interconnected via a switch

Each node has its own CPU with a sizable cache, a large main memory (typically>1GB) and a hd


Master: runs the file. Serves as the point system for the clustering S/W to route duties and monitor all individual nodes (i.e., slaves)

Beowulf: Open source s/w like LinuxMPI library for broadcasting and point-to-point

messages among the cluster’s nodes.


Phase 1: Distribute the entries of the fully-Phase 1: Distribute the entries of the fully-inverted index among the cluster nodes for inverted index among the cluster nodes for processing (e.g., round-robin distribution, processing (e.g., round-robin distribution, hash-based distribution).hash-based distribution).

Phase 2: Each cluster processes the Phase 2: Each cluster processes the containment query to generate the containment query to generate the corresponding lists of index entries.corresponding lists of index entries.

Phase 3: The elements of the generated Phase 3: The elements of the generated list are checked against one another to list are checked against one another to produce the result set.produce the result set.


Despite of XQuery we still need Java/.NET to:

implement user interfacescall Web services; interact with other

programsexpose functions as Web servicewrite complex applications

Trade-off between optimizability (on one side) & flexibility, determinism and expressive power (on the other side)

Query languages are more optimizable but pay a price on the other side

Imperative languages lack optimizability but the semantics are simpler, deterministic and richer


The ultimate goal: get rid of Java => all XQuery

XQueryP: Extension of XQuery for scripting

Server Application Logic (Java / .NET)

Web Service (XML Domain)

XML DB

XML

XQuery (XML Domain)


Client

Web Service

XML


Prototype in Big OracleDBPresented at Plan-X 2005

Prototype in BerkeleyDB-XMLMight be open sourced (if interest)

MXQueryhttp://www.mxquery.org (Java)Runs on mobile phones: Java CLDC1.1; some

cuts even run CLDC 1.0Eclipse Plugin available since March 2007

Zorba C++ engine (FLWOR Foundation)Small footprint, performance, extensibility,

potentially embeddable in many contexts


Ghassan Z. Qadah: ”Parallel processing of xml databases” [2005 IEEE CCECE/CCGEI]

Xiaogang Li, Swarup Kumar Sahoo, Gagan Agrawal: ”XQuery Perspective: Using XML/XQuery for Scientific Applications and Applying Scientific CompilationTechniques” [2004 SIGMOD]

Daniela Florescu, Donald Kossmann. ”CS345B: XML and Databases”. http://www.stanford.edu/class/cs345b/

W3C XML Query XQuery http://www.w3.org/XML/Query/


Introduces parts of code that will:Run in Sequential ModeDefine the order in which expressions will

be evaluatedBe strictly deterministicManually handle exceptions

CS315B

HealthCare Level Seven http://www.hl7.org/ Geography Markup Language (GML) Systems Biology Markup Language (SBML)

http://sbml.org/ XBRL, the XML based Business Reporting

standard http://www.xbrl.org/ Global Justice XML Data Model (GJXDM)

http://it.ojp.gov/jxdm ebXML http://www.ebxml.org/ e.g. Encoded Archival Description

Application http://lcweb.loc.gov/ead/ Digital photography metadata XMP An XML grammar for sensor data

(SensorML) Real Simple Syndication (RSS 2.0)


Xpath 1.0

XSLT 2.0XQuery 1.0

Xpath 2.0

XSLT 1.0

uses

uses

extends, almost backwards compatible

extendsFLWOR expressionsNode constructorsValidation

1999

2007


1. Allow to execute sub-computations in a different order

Parallelization, rescheduling2. Possible to use various data access paths3. Allow lazy evaluation4. Allow streaming/pipelining between operations (no

materialization of intermediate results)5. Allow various evaluation algorithms for the same

logical operation


xml databases

Documents