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Understanding XML Databases: Overview, Examples, and Query Languages

This comprehensive guide delves into XML databases, detailing their structure, querying capabilities, and practical applications. It covers fundamental concepts such as the tree structure of XML, XPath for navigation, and query languages like XML-QL and XQuery. Real-world examples highlight how to extract data from XML documents, illustrating the strengths and limitations of each querying approach. A comparison of relational databases versus XML-based systems is also provided, along with insights into storing XML databases. Enhance your knowledge of modern data management with this essential resource.

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Understanding XML Databases: Overview, Examples, and Query Languages

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  1. XML Databases by Sebastian Graf

  2. Table of Contents • XML Database Overview • XML Database Example • XPath • XML-QL • XQuery • Storing of XML Databases • Relational DB vs. XML • XML based Systems

  3. XML Database Overview • XML DB • Tree structure • Think in nodes & axes • Navigation in Tree • XPath

  4. 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>

  5. XPath • Describes how to process XML items • logical path to a node (location path) • Provides abstraction for XML languages • XSLT • XPointer • XQuery

  6. XPath /europe/country/name Selects all names • With predecessor „country“ • With predecessor „europe“

  7. 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

  8. XPath Conclusion • XPath offers basics navigation and selection features • However it is no complete XML Query Language • No joins possible

  9. Table of Contents • XML Database Overview • XML Database Example • XPath • XML-QL • XQuery • Storing of XML Databases • Relational DB vs. XML • XML based Systems

  10. XML-QL • Early proposal for XML Query language • Structure: • <Selection part> <construction part> • WHERE #### IN #### CONSTRUCT #### • Result : XML Document

  11. 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>

  12. XQuery • XQuery should extend functionality of XML-QL • Design was related to SQL • XQueries are of the form : FOR ### LET ### WHERE ### RETURN ### FLWR or Flower • Also possible:FOR-IN (FLWR) WHERE … (FLWR) … RETURN … (FLWR)…

  13. 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“) // country LET $cities := $c // city WHERE $c/@population > 1 000 000 AND count($cities) > 10 RETURN <bigcountry population = {$c/@population}> <name>{$c/@name}</name> {$cities} </bigcountry>

  14. 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}>

  15. XQuery – what is missing? • No data manipulation in version 1.0 • Raw Data has to be accessed for data manipulation • Planned for later versions: • Delete • Rename • Insert • Replace

  16. Table of Contents • XML Database Overview • XML Database Example • XPath • XML-QL • XQuery • Storing of XML Databases • Relational DB vs. XML • XML based Systems

  17. Storing of XML Databases • First Approach : one CLOB • Whole Database stored as value • Very easy to implement • SQL statements cannot be used for query • Second Approach : transformation • Transformation to Relations • SQL statements can be used • High transformation effort

  18. Relational DB vs. XML • The SilkRoute • Automatic transformation : relations  XML • Predefined DTD • Xperanto • Mapping of relational Database to XML • Adds XML functionality to DB2

  19. XML based Systems (B2B) • Software AG • Tamino • XML platform • Storing • Development • Integreation • eXcelon • Query interface for XPath

  20. More about XML databases Web & Datenbanken dpunkt.verlag by Erhard Rahm & Gottfried Vossen ISBN : 3-89864-189-9 BA Library : INF G 5100.62

  21. THE END Thanks for your attention

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