Portal and Workflow in Grid Computing: From Application Integration to Service Integration - Grid Computing: Infrastructure, Service, and Applications - page 279

• track resource usage;

• charge accounts for resource consumption;

• provide resource usage information.

11.2.4 Integration of AJAX into Portal Application

A single portal page may contain more than one portlet, which supply
content to the portal page. A disadvantage of portal is that portal page
refresh is an expensive operation as one portlet refresh can result in other
portlets refreshing at the same time. In order to tackle this problem, one
solution is to incorporate AJAX (Asynchronous JavaScript and XML) tech-
nology into the portlet. AJAX is a Web development technique for creating
interactive Web applications, and is one of the major enabling techniques
for Web 2.0 [25]. AJAX can improve the user experience and make Web
pages feel more responsive by exchanging small amounts of data with the
server behind the scene, so that the entire Web page does not have to be
reloaded each time when a user makes a request. This is meant to increase
the Web page's interactivity, speed, and usability.
AJAX is a combination of techniques such as JavaScript, DOM, XML,
and HTML/DHTML, which allows a Web browser to update parts of a
Web page asynchronously by communicating with a Web server using
JavaScript through an XMLHttpRequest component. By using AJAX, only
the data or the content is transferred over the networks where the data/
content is marshaled in XML format. The HTML structure and frame are
created locally within the Web browser using JavaScript. As each time
only the data are delivered rather than the whole Web page, users do not
have to reload the whole page to get a different dataset.
There are a number of open-source AJAX toolkits available such as
Direct Web Remoting (DWR) [1], Dojo [27], Google Web Toolkit [28],
Microsoft Atlas [29], Open Rico [30], Yahoo AJAX Library [31], and
Zimbra's Kabuki AJAX Toolkit [32]. These tools offer a number of
extremely useful user interface widgets and background tools for sim-
plifying the process of building an AJAX application. However, in terms
of a J2EE environment, most documentation and tutorials of these tool-
kits focus on building AJAX applications using servlets rather than port-
lets. Therefore, using these toolkits in portlets may cause some unexpected
hassles as the differences between servlets and portlets may result in
similar codes that are based on these toolkits or libraries working i ne
with servlets but not working properly with portlets. In order to facili-
tate the use of AJAX in a portlet application without depending on any
AJAX toolkits/libraries to avoid any unpredicted hassles, a develop-
ment model for the use of AJAX in JSR-168 portlets has been proposed
[33], as shown in Figure 11.1 . This model gives a clear view of how AJAX
works, which is not always explicitly clear in AJAX toolkits, and makes