Transform Documents with XQuery
XQuery is a new language under development by the W3C that’s designed to query collections of XML data. XQuery provides a mechanism to efficiently and easily extract data from XML documents or from any data source that can be viewed as XML, such as relational databases.
XQuery (http://www.w3.org/XML/Query) provides a powerful mechanism to pull XML content from multiple sources and dynamically generate new content using a programmer-friendly declarative language. The XQuery code in Example 2-12 (shakes.xqy) formats in XHTML a list of unique speakers in each act of Shakespeare’s play Hamlet. The hamlet.xml file can be found at http://www.oasis-open.org/cover/bosakShakespeare200.html.
Example 2-12. A simple XQuery to search Shakespeare (shakes.xqy)
<html><head/><body>
{
for $act in doc("hamlet.xml")//ACT
let $speakers := distinct-values($act//SPEAKER)
return
<span>
<h1>{ $act/TITLE/text( ) }</h1>
<ul>
{
for $speaker in $speakers
return <li>{ $speaker }</li>
}
</ul>
</span>
}
</body></html>This example demonstrates a
XQuery
FLWOR (pronounced flower) expression. The name
comes from the five possible clauses of the expression:
for, let,
where, order by, and
return. Example 2-12 says that for
every ACT element appearing at any level in the
hamlet.xml file, let the
$speakers variable equal the distinct values of
all the SPEAKER elements found under that instance
of ACT. Then for every $act and
$speakers value, return the
$act’s TITLE
text using an h1 element ...
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