xml-dev - Re: Is there anyone working on a binary version of XML?

["Rick Jelliffe" <ricko@allette.com.au>]

 From: Stephen D. Williams <sdw@lig.net>

>> Tim Bray wrote:
 >>         There are two distinct issues 1) efficiency of parsing  2)
compactness. A
>> standard compression format for XML (ala zip,gzip etc) would be for
>> bandwidth limited applications.

Someone at ITU (International Telegraph Union) was working on an ASN.1
compression of XML markup. I think they may have opted for the WAP
method, for compatability. (I think the use of ASN.1 means fixed DTDs.)

I have done a few tests on how much compacter forms of XML (e.g.
shortrefs) impact arrival characteristics of document packet-groups
under TCP/IP compared to compression.  If your packet size is small, and
you really need to get at data in the first packet (so that you can
piggy back request for auto-linked resources in with the ACK for the
first packet group), then more compact forms of markup may make a
difference. But in general, compression is more effective. (It also
depends on where the bottlenecks are in your data path.)

One trivial way to minimise file sizes for transmission is to collapse
white-space inside markup (e.g. [\ \t \n\ r]+ becomes [\n]), to make
sure that newlines are not CR LF pairs, and to minimize whitespace in
data: (removing trailing spaces, [\ \t]+\n) becomes [\n], is a safe
transformation, for example.) And select your element and attribute
names so that their length is inverse to their frequency, as much as
possible: so use "a:s" not "abracadabra:shazamarama" (you may even make
two versions of your DTD: an authoring one and a transmission one.) One
pof the main bottleneck on many SOHO systems is the modem speed:
reducing the end-to-end character count means fewer packets, and more
data arrives earlier, so more auto-links are followed earlier.


Rick Jelliffe


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