Portal and Workflow in Grid Computing: From Application Integration to Service Integration - Grid Computing: Infrastructure, Service, and Applications - page 274

portal is built upon the familiar Web portal model, such as Yahoo or
Amazon, to deliver the benei ts of grid computing to virtual communities
of users, providing a single access point to grid services and resources.

11.2.1.2 Grid Portal: Nonportlet Based versus Portlet Based

According to the way of building portals, grid portals can be classii ed
into nonportlet based and portlet based [3]. Many early grid portals or
early version of existing grid portals are nonportlet based; for example,
the Astrophysics Simulation Collaboratory (ASC) portal [4] and UNICORE
[1,5]. These grid portals can provide uniform access to the grid resources.
Usually these portals were built based on typical three-tier Web architec-
ture: (1) Web browser, (2) application server/Web server which can handle
HTTP requests from the client browser, and (3) back-end resources that
include computing resources, databases, and so on.
Portlet-based portals have become one of the most exciting areas for the
portal server platform in recent years [6]. A portlet is a Web component
that generates fragments—pieces of markup (e.g., HTML, XML) adhering
to certain specii cations. Fragments are aggregated to form a complete
Web page. The portlet-based portal is based on component-based devel-
opment, and portlets in the portal are engineered independently from
each other. A portlet is an individual class that processes the user request
and returns the content for display within a portal. It is contained in port-
let container, which is part of portal and instantiates and executes the
portlet classes.
Developing portlet-based portals can bring many benei ts to both end-
users and developers, which now gets more recognition [8]. This can be
rel ected through evolution of some grid portal projects. For example,
although the ASC portal [4] did provide functionalities for the astrophys-
ics community to remotely compile and execute applications, it was difi -
cult to maintain when the underlying supporting infrastructure evolved.
Eventually, the ASC portal was retired and its functionality moved into
the Cactus portal developed by adopting GridSphere [2]. Another example
is the GridPort portal [4]. The early GridPort was implemented in Perl and
made use of HotPage [9] technology for providing access to grid access.
Now the GridPort adopts GridSphere.

11. 2 .1. 3 Portlet Standards

One of the main advantages of using a portlet-based portal is that there are
two standards for portlet development, namely JSR-168/JSR-286* and WSRP
(Web Service for Remote Portlets). JSR-168 establishes a standard API for

* JSR 286 is an extension of JSR-168. In this chapter, the JSR-168 is used for the standard
portlet.