EXI WG review of Mobile Web Application Best Practices PR

Dear Mobile Web BP WG members,

On behalf of the EXI WG, I would like to send in the following comment 
that reflects our review of the document [1] with primary emphasis on section
3.4.1 Use Transfer Compression where the use of EXI is described, from 
the technical viewpoint concerning EXI.

We felt that some of the descriptions given in relation to EXI in section 3.4.1.2 
may as well be moderated when it associates EXI with limitations/restrictions 
that are generally true for other representations and compression techniques, 
but not necessarily outright so for EXI. The cause for EXI in fact was to some 
extent to overcome those impediments that relate to processing efficiency, 
battery usage, and the effectiveness on small messages. The rest of this message 
below describes some characteristics of EXI, which we hope will better inform the 
document in a way to build on what is already described in the section and 
improve it to result in more accurate characterization of EXI as it relates to 
the topic discussed in the section.

When the content being transferred is XML in particular, the HTTP content-
coding parameter value "exi" [2] enables the use of EXI where it is supported.
EXI is known to make additional benefit available for a diverse use cases of
XML document exchanges that range independently in aspects such as document
sizes (including very small files of less than 1k in size), and resourcefulness
(such as footprint, battery capacity or CPU excellence) of the devices.

EXI streams are observed to be processed consistently faster than the equivalent
text XML streams can be processed by XML parsers. This is in addition to the file
size benefit that EXI provides. EXI's compression feature compresses XML files
more compact than gzip or DEFLATE can achieve, and the compressed EXI streams
can be decompressed much faster than decompressing streams that were generated
by gzip or DEFLATE compressions. Section 3 of EXI Evaluation Note [3] describes
the advantages of EXI that are exhibited consistently across broad range of document
types from diverse use cases differing in sizes, styles, etc.

This way, EXI uses both processor cycles and network bandwidth more efficiently,
the combination of which makes EXI very amenable to the efficient use of battery,
where reduced bandwidth translates into reduced the power consumption for sending
or receiving the file while the reduced processor cycles can save the power
necessary for processing the file, and the two power conservations add up
simultaneously.

[1] http://www.w3.org/TR/2010/PR-mwabp-20101021/
[2] http://www.iana.org/assignments/http-parameters/
[3] http://www.w3.org/TR/2009/WD-exi-evaluation-20090407/#results

Best regards,

Taki Kamiya for the EXI Working Group

Received on Tuesday, 16 November 2010 20:36:56 UTC