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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<title>Introduction</title>
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<h2>Who is this tutorial for?</h2>
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<p>This tutorial is for people who want to build interactive client-server
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functionality where a web-browser is the client. It will show you how to build
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a live, interactive chat application that requires nothing more than a web
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browser that supports JavaScript.</p>
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<p>The interesting thing about a chat application, which shows why Nevow Athena
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is special, is that it involves two-way communication. In other words, it
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involves not only the recently-popular AJAX (the web browser sending commands
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to the server without loading a new page) but also the trickier and, in our
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opinion, somewhat cooler technique known as COMET (the web server
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sending commands to the <em>browser</em>).</p>
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<h2>Who is this tutorial <em>not</em> for?</h2>
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<p>Nevow Athena is <em>not</em> for people who want a normal web application
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framework. If you want one of those, you should use
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non-Athena-<a href="http://divmod.org/trac/wiki/DivmodNevow">Nevow</a>,
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<a href="http://www.djangoproject.com/">Django</a>,
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<a href="http://turbogears.org/">TurboGears</a>, or maybe even
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<a href="http://rubyonrails.org/">Ruby On Rails</a>. Athena doesn't work in terms
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of pages, links, or HTTP requests and responses; it is a client-server
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framework that works in terms of widgets, JavaScript objects, and symmetric
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asynchronous message queues.</p>
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<p>However, as alluded to above, Athena is part of a larger framework, Nevow,
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which can be used to build more general-purpose and <q>traditional</q>
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<p>AJAX isn't a technology in and of itself, bur rather an amalgam of
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technologies used together in order to accomplish the goal of making web
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applications more responsive than traditional delivery and interactive
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mechanisms, such as HTML forms submitted to a server.</p>
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<p>In particular, AJAX consists of the following:</p>
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<li>Asynchronous communications from a user's browser to a server</li>
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<li>Exchanged data (usually XML or JSON)</li>
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<p>Historically, the focus of AJAX technologies was user-event driven. However,
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with the need to update the user's browser with events generated at the server,
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a solution more sophisticated than AJAX was needed; this has been dubbed COMET.
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Athena is implemented using both AJAX and COMET techniques, and therefore
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allows two-way browser <-> server communications.</p>
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<h2>Athena Basics</h2>
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<p>We've provided brief background information on AJAX/COMET, but what is the
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purpose of Athena? What makes Athena different than other solutions? Here are a
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few key points that should help with these questions::</p>
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<li>Athena exists to make writing COMET web applications easy.</li>
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<li>Athena is written in Python and JavaScript</li>
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<li>It is written to be used with Nevow, a <a
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href="http://twistedmatrix.com/">Twisted</a>-based web framework.</li>
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<li>Similar to Twisted's <a
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href="http://twistedmatrix.com/projects/core/documentation/howto/pb-intro.html">Perspective
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Broker</a>, Athena employs remote calls.</li>
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<p>Athena was written by Twisted and Divmod developers (in addition to
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contributing members of the community) in order to bring the outdated and
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Nevow-incompatible Woven LivePage technology to Nevow. In addition, it was an
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opportunity to improve upon the original design and incorporate new features to
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address the growing needs of developers.</p>
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<h2>Target Applications</h2>
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<p>Good candidates for Athena web applications would include those where the
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application needs to respond to user input and/or updates from servers, such
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<li>conference software (e.g. whiteboard, shared text, chat, etc.)</li>
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<li>interactive, multi-player games</li>
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<li>social networking tools</li>
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<li>office applications (e.g., spreadsheets, word processors, etc.)</li>
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<h2>Target Developers</h2>
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<p>Anyone who wants to create interactive, web-based applications is a
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potential Nevow/Athena user. It's best to have some background in writing web
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applications, and in addition, to know how to use Nevow. However, we hope that
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this tutorial will be just as useful for beginners as experienced
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