Re: [apps-discuss] +exi
Peter Saint-Andre <stpeter@stpeter.im> Tue, 13 December 2011 22:36 UTC
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Date: Tue, 13 Dec 2011 15:36:11 -0700
From: Peter Saint-Andre <stpeter@stpeter.im>
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To: Carine Bournez <carine@w3.org>
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Cc: paduffy@cisco.com, "apps-discuss@ietf.org" <apps-discuss@ietf.org>, Thomas Herbst <therbst@silverspringnet.com>
Subject: Re: [apps-discuss] +exi
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On 12/13/11 2:58 PM, Carine Bournez wrote: > On Tue, Dec 13, 2011 at 10:45:19AM -0700, Peter Saint-Andre wrote: >> I chatted with a few folks about this in Taipei and afterward. >> >> As I understand it (correct me if I'm wrong), EXI has two modes: >> >> 1. Straight compression of the text representation of XML (text in, >> EXI-compressed data out). To make use of the data, you then decompress >> it back into the angle-brackety text representation of XML that we all >> know and love. >> >> 2. Direct, binary representation of the XML infoset. In this case, you >> never have the data in a angle-brackety text representation, instead it >> is always a binary representation. > > It is not exactly 2 modes. The EXI 1.0 Recommendation only specifies a > compressed encoding of an XML Infoset. Applications that include an EXI > processor may use different approaches around the encoding/decoding process. > So, you can have applications with a (text) XML document as an input > (what you describe as #1), and applications that never use a text > serialization (your #2). > >> It seems to me that #1 is similar to gzip, i.e., the textual >> representation is encoded using EXI compression, so we'd have this: >> >> Content-Type: application/foo+xml >> Content-Encoding: exi >> >> It seems to me that #2 might not be an encoding of the relevant +xml >> content type, but might be a different content type, so +exi might be >> appropriate. > > The W3C EXI Working Group has decided not to follow the +exi path, > since it involved a potentially infinite number of types to register. > There could also be conformance issues: an EXI stream not encoded > from a text version might not be necessarily serialized as a conformant > "foo" after decoding from its EXI form. It needs some specification > work for each foo+exi. > The generic application/exi content-type is meant to be used for cases > where there is no serialization from/to a standard format (then no > content-type can be used), as well as for protocols that have no > content-encoding capability. Thank you for the clarifications. The example that raised this issue for me was the ZigBee Alliance Smart Energy Profile 2.0, which supports both a text serialization of their XML format and an EXI representation. Tom Herbst and Paul Duffy can describe that use case more accurately than I can, but based on what you've said it seems that they would use application/sep+xml and note a content encoding of EXI for the second case. However, it is possible that (if their transport/transfer protocols do not have a way to note the content encoding) they might use application/exi for the second case. I'll let Tom and Paul speak to that. Zach Shelby might also have opinions in the matter. In any case, I think they have the information they need to make the right decision in the ZigBee Alliance (and if not they can speak up). Peter -- Peter Saint-Andre https://stpeter.im/
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- [apps-discuss] +exi (was: Re: type name suffixes) Peter Saint-Andre
- Re: [apps-discuss] +exi (was: Re: type name suffi… Bjoern Hoehrmann
- Re: [apps-discuss] +exi Peter Saint-Andre
- Re: [apps-discuss] +exi (was: Re: type name suffi… Zach Shelby
- Re: [apps-discuss] +exi (was: Re: type name suffi… Mark Nottingham
- Re: [apps-discuss] +exi (was: Re: type name suffi… Carsten Bormann
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- Re: [apps-discuss] +exi Peter Saint-Andre
- Re: [apps-discuss] +exi SM
- Re: [apps-discuss] +exi Peter Saint-Andre
- Re: [apps-discuss] +exi Julian Reschke
- Re: [apps-discuss] +exi Carine Bournez
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- Re: [apps-discuss] +exi Peter Saint-Andre
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