Let's look at examples. For this, we will use Zorba, a “NoSQL” processor.

Every XPath expression is also a legal XQuery.

1. path-Authors
2. path-AuthorsURI
3. path-FirstAuthors
4. path-BigPaper

Of course, XQuery syntax is more flexible and more expressive.

5. query-titles
6. query-AuthorsURI
7. query-FirstAuthors
8. query-VeryFirstAuthor
9. query-VeryFirstAuthor-let
10. query-Portfolios
11. query-PortfoliosSession
12. query-PortfoliosCount
13. query-DistinctAuthors-fn
14. query-DistinctAuthors-groupby
15. query-DistinctPortfoliosCount

Using Zorba, having an XQuery query in a file query, I can run these from the command line.

% zorba --indent -f -q query

• bibliography.xml
• bibliography-pretty.xml (with whitespace, for readability)

Here are a few leads on tracking down interesting XML data sources (data sets).

• www.xmldatasets.net
  Lots of dead links, unfortunately, but many good sources too. U.S. Census is interesting data.

• explore.data.gov
  This provides many U.S. government resources as provided by the Open Government Initiative.

• Medline Plus
  This provides information on health topics. It is a service of the U.S. National Library of Medicine.

• EIONets' Airbase
  Information on air polution tracking countries in Europe.

• CIA World Factbook in XML
  Provided on SourceForge.

• University of Washington's XML Data Repository.

You likely will want an XQuery engine to play with, for validating your XQuery queries, and for producing the results for your integration tasks. You are welcome to use any available engine, or online XQuery engine for the task, that supports at least XQuery 2.0.

In class, I have been using Zorba. Available well supported, open source XQuery engines are

• BaseX:
  a native XML database system with XQuery. (Requires a server to be running.)
• eXist:
  a native XML database system with XQuery. (Requires a server to be running.)
• XQilla:
  Supports XQuery. (A native XML database system, I believe.)
• Zorba:
  a stand-alone, command-line XQuery evaluator.

Zorba is up and running on indigo and red! Special thanks to Paul, Seela, and the tech team of EECS for putting this up.

The other way to run XQuery is to expose it in a web broswer through JavaScript, such as Firefox, which has the facilities hidden underneath. While XPath is readily available through JavaScript, XQuery is not. This is a bit messy, but convenient, and quite fun.

XPath Checker is the plug-in in Firefox for xpath that I used in class for doing xpath queries.

XQIB provides a JavaScript “library” that makes running XQuery in the browser accessible. One grabs the mxqueryjs — which contains mxqueryjs.nocache.js — and plants it under one's www-site. Or link it remotely in your www-page containing an XQuery query. (You could link to mine in the example below.)

See titles.html under my www home directory as an example. Look at its source. It queries the title nodes out of the bibliography.xml example file (a local copy, in this case).

This approach has extra complications.

• Because of name space issues — the default name space within the HTML document is for the HTML document itself, not the source XML document you are querying — in the XQuery query, node calls have to provide a proper name space, or wildcard it so any name space will match. E.g., $mydoc//*:title instead of just $mydoc//title.

• How to return the results? Easiest is to modify the HTML page to display them. This requires modifying the DOM of the page, and the results should be cast as HTML rather than general XML, so the browser will render the results correctly. (The example shows this.)