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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 Schema
2. 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?