XQuery: The Search Language For A Multi-Platform Future
The advent of wireless internet access has made web design a very
complicated matter. Previously, all web browsers were created equal.
HTML was the only language used to create web sites, and it was only
possible to go online with a desktop PC.
Since the turn of the century, cyberspace has changed. It is now
possible to surf the world wide web using a wide variety of wireless
gadgets, such as cell phones, palm tops, laptops, computer screens in
automobiles, etc. As a result, new programming languages and
specifications that are more versatile than HTML have evolved to create
websites that can be displayed on the new web browsers utilized by these
various devices.
Languages such as XML, XHTML, XSL, and a host of other programming
innovations were developed because web sites coded in basic HTML were
not being displayed properly on the browsers installed on all these neat
gadgets. XML is a language that enables data to be displayed across all
platforms because XML is a simple text file that merely defines data, it
does not tell the web browser how to display the data. XSL and XHTML
were created so that XML could be transformed into a web page.
Now that you have a basic understanding of how and why programming has
changed, you are ready for a brief introduction to the main topic of
this article, XQuery. XQuery was invented so that there was a way to
query data stored in an XML document, much the same way SQL is used to
query a database.
XQuery uses simple functions to query a document. An XQuery function
looks a little like a javascript function in that it uses parentheses
containing an element that is to be the object of the function. With
XQuery, the element in parentheses is typically the name of the document
or file to be queried.
To find what it is looking for within that file, XQuery narrows its
search by using path expressions that look a lot like the path for an
ordinary file stored on your computer, with the various subsets of data
within the XML file separated by backslashes. The predicate is the final
component of an XQuery function. The predicate tells the function
exactly what information, data, or range of data within a particular
subset is to be extracted and returned to the user.
For example, an XML file for a dating website would contain a list of
men and women who have posted their profiles on the website. Some of the
people in the XML file might be classified as single, while others might
classified as divorced. The XML file would also contain the age of each
man and woman.
If a woman were to visit that dating website and perform a search for
profiles of only single men who are over the age of 30, that search
request would be converted into an XQuery function that would contain a
path that would tell the function to search through the list of men who
are classified as single, and the predicate would instruct the function
to return only the profiles of the single men who are older than 30.
Learning how to use XML, XHTML, and XQuery is of critical importance to
every web designer or programmer. There are now so many ways to connect
to the internet using computers that run on different platforms that are
no longer compatible with many elements of the HTML programming
language. Web designers need to be conscious of this and start designing
web sites that utilize XML and XQuery.
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Author: Jim Pretin
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