XQuery is a new query language for XML data. It provides functions for gathering XML from variety of sources including files, URLs, etc and performing SQL style operations on them. One of the most basic yet impressive abilities is the ability to join between multiple documents. For instance, assume that there are two XML documents: a book catalog from Amazon and a similar catalog from Barns and Noble (the XML does not have to follow the same schema, in this example one retailer uses the ?book? element for each book in the catalog while another uses ?entry?, etc). The following XQuery expression joins both sources on the book ?title? element and displays all books that are more expensive at Barns and Noble
for $b in $catalog1//book, $a in $catalog2//entry
where $b/title = $a/title and $b/price > $a/price
XQuery is also capable of manipulating free-standing XML documents similar to XSL using its FLOWR language.
The XQueryService integrates XQuery API with the ESB and allows it to feed parameters from and write output to various parts of the JMS/XQ message. Actually, the ability to take parameters from XQParts, JMS properties, and literal values (as well as writing results to JMS properties and message parts) is quite useful for many other services so this project includes a tiny framework that allows reusing that functionality.
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