August 2007
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August 26, 2007

Mobile Ajax Workshop position paper

Filed under: ajax — Mark Baker @ 11:09 am

This is the position paper we recently submitted to the W3C/OpenAjax Workshop on Mobile Ajax.

The best mobile Ajax application …

is the one that’s never written

A position paper for the
Workshop on Mobile Ajax

by Mark Baker of

Hypertext inventor Ted Nelson talked about “the two Gods of literature”[1],
publisher and reader, and the battle between them in determining what the
reader ultimately consumes.  Traditional Web programming with HTML and
CSS (no script) provides effectively equal power to each God, permitting the
publisher to provide the content together with declarations about how that
content could be presented, but enabling the reader to instruct its
agent to ignore and/or extend those declarations as it sees fit. 
Scripting, on the other hand, puts all the power in the hands of the
publisher, providing the reader two options; either execute it to be able
to consume the content it contains, or don’t and don’t.

The “reader power” afforded by declarative programming is especially important
for mobile use for at least two reasons.  First, it allows the
user agent to repurpose the content so it can be presented to the user in
the context of the particular nuances of the input and output methods of
the device.  Second, it allows the user agent to be shipped
with code which is optimized for the processing of the predefined
markup language, where “optimized” can be along any dimension: speed, size,
battery consumption, etc..

Fortunately, there exists an approach which permits us to have the best of
both worlds.  If we factored out the commonly used script components, and
extended HTML so that those components could be instantiated declaritively,
then we could use declarative programming for these common components but
continue to use script for the less common cases.  As an example, “drag
and drop” is a reasonably common feature implemented by scripts, but could
easily be accomplished via a declarative approach [2].

One downside of this hybrid approach is that standardization of the
extensions – and deployment of software which uses them – can take a very long
time.  However it is not as big a problem as it first seems. 
Somewhat ironically, we can use script to help us incrementally deploy
declarative content, by associating that content with script
which interprets and processes the extension tags when browsers don’t support
them (see [2] again for an example of this).

Some Javascript toolkits already provide for a somewhat similar approach, at
least regarding the binding of HTML extensions to script. 
Dojo includes “Dijits” (Dojo widgets) which permits, for
example, HTML forms to be extended with attributes whose value explicitly
references a Dojo-specific scripted TextBox widget.  Once the Dojo
libraries are linked in, the extended processing occurs.  All Dijits seem
to be missing is to acknowledge the value of standardizing their HTML

HTML 5 (ne a bunch of WHAT WG specs) can also be seen in a new light when
considering its role in this proposed approach.  It defines
(amoungst other things) a number of extensions that aim to do in a declarative
manner what is currently done with script.  For example, in-browser form
validation.  The approach outlined here also suggests that there
would be value in developing a script which could process the HTML 5
extensions for HTML 4 browsers.

Note: see also the TAG’s view on declarative vs. imperative, in their Rule of
Least Power finding[3].

 [1] Theodore Nelson.  The Future of Information: Ideas,
Connections and the Gods of Electronic Literature.  ASCII Corp,
1997.  Unpublished.



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