[Members] EXI over XMPP

Peter Waher Peter.Waher at clayster.com
Wed Mar 14 19:04:22 UTC 2012


Ok

I had a look at the EXI extension stub:
http://xmpp.org/extensions/inbox/compress-exi.html

There are several points where this has to be extended for it to work properly. EXI can work in several modes, with different levels of compression results. And both parties (three parties in the case of XMPP: 2 clients and 1 server) need to agree on which rules to apply:

1) Schema-less "binarization" of XML (documents or fragments)
2) "Binarization" of XML, using knowledge of schemas. (All parties need to use the same schemas - so an agreement has to be made, perhaps only on namespace?) More efficient than (1), in cases where schemas exist. If one of the parties lacks a schema, method in (1) has to be used.
3) (2) sequenced into different buckets and further compressed (zip). More efficient than (2).

There are also a small set of parameters that participants need to agree on.

We're implementing an EXI stack into our system for other purposes, and we would like to be able to use EXI over XMPP also, if we could find a server supporting it. We also have contacts with parties developing sensors for IPv6 sensor networks for small embedded wifi devices. They're today usig CoAP instead of XMPP, for its minimal implementation footprint. However, EXI over XMPP would be an interesting alternative in such cases where communication buffers are small.

If somebody wakes the EXI-project to life again, I'd like to participate. I can contribute with knowledge about EXI and what type of handshake procedure needs to take place for all parties to agree.

(Also, an optional method of interchanging schemas would be nice. It would allow more competent systems to in runtime adapt its EXI compression to schemas defined by other parties. Perhaps as a part of a separate extension.)

Sincerely,
Peter Waher

-----Original Message-----
From: Peter Saint-Andre [mailto:stpeter at stpeter.im] 
Sent: den 14 mars 2012 13:51
To: XSF Members
Subject: Re: [Members] EXI over XMPP

On 3/14/12 6:49 AM, Ralph Meijer wrote:
> On 2012-03-14 09:28 , Peter Waher wrote:
>> Hello
>>
>> Does anyone know of an XMPP Server that supports EXI (i.e. binary 
>> compressed XML)?
>>
>> http://www.w3.org/XML/EXI/
>>
>> Or if anybody is considering working with EXI?
>>
>> EXi is an efficient way to encode and compress XML, and is well 
>> suited for small embedded devices (like sensors) for coding/decoding data.
>> There are code generators that generate efficient C++ code given XML 
>> Schema files as input.
> 
> Ah, is it that time of year again? :-D
> 
> I very much doubt anyone has pursued this. In 2008 there was some 
> discussion [1] on a proposed XEP [2] for this and was rejected [3] by 
> the council.
> 
> 
> [1]
> <http://mail.jabber.org/pipermail/standards/2008-February/thread.html#
> 17938>
> 
> [2] <http://xmpp.org/extensions/inbox/compress-exi.html>
> [3] 
> <http://mail.jabber.org/pipermail/standards/2008-March/018185.html>

Ah yes. As I recall, I did reach out to EXI experts and didn't receive any feedback. If there's interest, I can do that again (now that I am in more frequent communication with W3C folks).

Peter

--
Peter Saint-Andre
https://stpeter.im/




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