Introduction to XQuery

XQuery is about extracting information from XML documents.

What You Should Already Know

Before you study XQuery you should have a basic understanding of XML and XML Namespaces.

If you want to study these subjects first, please read our XML Tutorial.

What is XQuery?

• XQuery is a language for querying XML data
• XQuery is built on XPath expressions
• XQuery for XML is like SQL for databases

XQuery is About Querying XML

XQuery is a language for finding and extracting (querying) data from XML documents.

Here is an example of a question that XQuery could solve:

"Select all CD records with a price less than $10 from the CD collection stored in the XML document called cd_catalog.xml"

XQuery and XPath

XQuery 1.0 and XPath 2.0 shares the same data model, the same functions, and the same syntax.

If you have already studied XPath you will have no problems with understanding XQuery.

You can read more about XPath in our XPath Tutorial.

XQuery is Not (yet) a Web Standard

XQuery 1.0 is still a W3C Working Draft.

It is expected to reach a W3C Recommendation status early in 2004.

To read more about the XQuery activity at W3C, please read our W3C Tutorial.

XQuery Example

Let's try to learn some XQuery by an example.

The XML Example Document

We will use this XML document called "books.xml" in all our examples:

<?xml version="1.0" encoding="ISO-8859-1"?>

<bib>

<book year="1994">  <title>TCP/IP Illustrated</title>  <author><last>Stevens</last><first>W.</first></author>  <publisher>Addison-Wesley</publisher>  <price>65.95</price></book> <book year="1992">  <title>Advanced Programming in the Unix environment</title>  <author><last>Stevens</last><first>W.</first></author>  <publisher>Addison-Wesley</publisher>  <price>65.95</price></book> <book year="2000">  <title>Data on the Web</title>  <author><last>Abiteboul</last><first>Serge</first></author>  <author><last>Buneman</last><first>Peter</first></author>  <author><last>Suciu</last><first>Dan</first></author>  <publisher>Morgan Kaufmann Publishers</publisher>  <price>39.95</price></book> <book year="1999">  <title>The Technology and Content for Digital TV</title>  <editor>    <last>Gerbarg</last><first>Darcy</first>       <affiliation>CITI</affiliation>  </editor>  <publisher>Kluwer Academic Publishers</publisher>  <price>129.95</price></book> </bib>

Click here to view the XML file in your browser

Extracting Nodes With a Functions

XQuery uses functions to extract data from XML documents.

The following XQuery: