XQuery

How to handle databases with the XML standard?

Peter van Keeken

Industrial trainee, Evitech

4th period 2002

What is XQuery?

XQuery is a data query language for

XML designed by W3C.

XQuery is designed to be broadly applicable across all types of XML data sources

(eg. Databases).

XQuery history

XQuery is derived from Quilt• an XML query language • which borrowed features from languages like:

– XPath 1.0 – XQL (XML Query Language)– XML-QL (a query language for XML)– SQL (Structured Query Language)– OQL (ODMG, Object Database Standard)

XQuery specifications:

• Able to query databases and data from (XML) documents

• XQuery is a data model describing how a XQuery processor should process an XML document or datasource that is available to an XQuery processor.

• XQuery is also based on:1. XML Schema2. XPath (version 2.0)

• a human-readable syntax and an XML-based syntax is required

More practical decription:

• Allows joins between XML documents• Allows sorting and grouping• Language is SQL like but works on

trees rather then relational tables

An simple example:

• You have for instance the next list of recipes in an XML Document: recipes.xml

• Example XQuery:FOR $t IN document (“recipes.xml”) // title

RETURN $t

• The result:The query will return all the titles

of the recipes in the file.

Another example:• A more complex query based on the same resource:

recipes.xml

• Example XQuery:FOR $i IN distinct(document("recipes.xml") //ingredient/@name)

RETURN <ingredient name={$i}>

{ FOR $r IN document("recipes.xml")//recipe

WHERE $r//ingredient[@name=$i] RETURN $r/title

}

</ingredient>

• The result:The query will return for each ingredient,

the recipes that it is used in.

The Good about XQuery

• Can store document or data style XML• Tremendous flexibility• Complement RDBMS with XML mapping

solutions• Performance can be very good

The Bad about XQuery

• Standard is still in development• Techniques are unfamiliar to people• Not good at transaction processing• Some expected database practices are still

unsupported• Interoperability between products is minimal

Resources:

WWW:• www.w3.org/TR/xquery/• people.cs.uct.ac.za/~agelderb/hons/coursXMLAarhus.pdf

Book (for XML Schemas):D. Hunter, Beginning XML, 2nd Edition, Wrox P2P serie

THE END

Questions?