PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

860 Chapter 34 Building Web 2.0 Applications with Ajax
Server-Side Programming
Server-side programming includes all scripts that reside on a web server and are interpreted
or compiled before sending a response to the client. Server-side programming
typically includes server-side connections to databases; requests and responses to and
from a database are thus part of the scripts themselves.
These scripts could be written in any server-side language, such as Perl, JSP, ASP, or
PHP—the latter being the language used throughout the examples in this chapter for
obvious reasons. Because the response of a server-side script is typically to display data
marked up in some variant of standard HTML, the end-user environment is of little
concern.
XML and XSLT
You were introduced to XML in Chapter 33,“Connecting to Web Services with XML
and SOAP,” which included basic information on the format, structure, and use of XML.
In the context of Ajax applications, XML—the “X” in Ajax—is used to exchange data;
XSLT is used to manipulate the data.The data itself is either sent through or retrieved
from the Ajax application you create.
For more information on XML, see http://www.w3.org/XML/, and for more information
on XSL, see http://www.w3.org/TR/xslt20/.
Fundamental Ajax
Now that you’ve learned the possible constituent parts of an Ajax application, this section
will put those pieces together to produce a working example of this technology in
action. Keep at the forefront of your mind one of the main reasons for using Ajax in the
first place: to produce interactive sites that respond to user actions but without the interruption
that comes from refreshing an entire page.
To achieve the this goal, an Ajax application includes an extra layer of processing that
occurs between the requested web page and the web server responsible for producing
that page.This layer is commonly referred to as an Ajax Framework (also an Ajax
Engine).The framework exists to handle requests between the user and the web server,
and it communicates the requests and responses without additional actions such as
redrawing a page and without interruption to whatever actions the user is currently performing,
such as scrolling, clicking, or reading a block of text.
In the next few sections, you’ll learn how the different parts of an Ajax application
function together to produce a streamlined user experience.
The XMLHTTPRequest Object
Earlier in this chapter, you learned about HTTP requests and responses and also how
client-side programming can be used within an Ajax application.The specific JavaScript
object called XMLHTTPRequest is crucial when connecting with the web server and making
a request without entirely reloading the original page.