XML Databases

by Sebastian Graf

Table of Contents

XML Database OverviewXML Database ExampleXPathXML-QLXQueryStoring of XML DatabasesRelational DB vs. XMLXML based Systems

XML Database Overview

XML DBTree structureThink in nodes & axes

Navigation in Tree XPath

XML Database Example<europe>

<country car_code = D memberships = org-eu org-nato …>

<name>Germany</name>

<capital>Berlin</capital>

<poulation> 82 440 134</population>

<country code>de</country code>

<bundesland>

<name>NRW</name>

<capital>Düsseldorf</captial>

<population>18 052 000 </population>

</bundesland>

</country>

</europe>

XPath

Describes how to process XML items logical path to a node (location path)

Provides abstraction for XML languagesXSLTXPointerXQuery

XPath

/europe/country/name

Selects all namesWith predecessor „country“

With predecessor „europe“

XPath examples

/europe/country[population > 50 000 000]

All countries with population > 50 000 000

/europe/country/@car_code

All car_codes of Europe

/europe/country[name = Germany]//capital

All captials in Germany

XPath Conclusion

XPath offers basics navigation and selection features

However it is no complete XML Query LanguageNo joins possible

Table of Contents

XML Database OverviewXML Database ExampleXPathXML-QLXQueryStoring of XML DatabasesRelational DB vs. XMLXML based Systems

XML-QL

Early proposal for XML Query languageStructure:

<Selection part> <construction part>WHERE #### IN #### CONSTRUCT ####

Result : XML Document

XML-QL Example

WHERE <country car_code=$id><name>$name</>

</>IN “…/europe.xml“CONSTRUCT <country car_code=$id name=$name</>

<result><country car_code=“D” name=“Germany”></><country car_code=“F” name=“France”></>…..

</result>

XQuery

XQuery should extend functionality of XML-QL

Design was related to SQLXQueries are of the form :

FOR ### LET ### WHERE ### RETURN ###

FLWR or FlowerAlso possible:

FOR-IN (FLWR) WHERE … (FLWR) … RETURN … (FLWR)…

XQuery example

Task : find all countires, that have a population > 1 000 000 and have at least 10 cities

FOR $c IN document(„europe.xml“) // countryLET $cities := $c // cityWHERE $c/@population > 1 000 000

AND count($cities) > 10RETURN <bigcountry population = {$c/@population}>

<name>{$c/@name}</name>{$cities}

</bigcountry>

XQuery Join example

Task : find all pairs of countires and cities, that have the same name

FOR $country IN //country, $city IN //city

WHERE $country/name/text() = $city/name/text()

RETURN <pair name={$country/name/text()}

country={$country/@car_code}

city={$city/@country}>

XQuery – what is missing?

No data manipulation in version 1.0Raw Data has to be accessed for data

manipulation

Planned for later versions: Delete Rename Insert Replace

Table of Contents

XML Database OverviewXML Database ExampleXPathXML-QLXQueryStoring of XML DatabasesRelational DB vs. XMLXML based Systems

Storing of XML Databases

First Approach : one CLOBWhole Database stored as valueVery easy to implementSQL statements cannot be used for query

Second Approach : transformationTransformation to RelationsSQL statements can be usedHigh transformation effort

Relational DB vs. XML

The SilkRouteAutomatic transformation : relations XMLPredefined DTD

XperantoMapping of relational Database to XMLAdds XML functionality to DB2

XML based Systems (B2B)

Software AGTamino

XML platform Storing Development Integreation

eXcelon Query interface for XPath

More about XML databases

Web & Datenbanken

dpunkt.verlag

by Erhard Rahm & Gottfried Vossen

ISBN : 3-89864-189-9

BA Library : INF G 5100.62

THE END

Thanks for your attention