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[LC-2185] RE: Question about EXI Draft - XML declaraion

From: Taki Kamiya <tkamiya@us.fujitsu.com>
Date: Wed, 7 Jan 2009 12:12:06 -0800
To: "'TAMIYA Keisuke'" <tamiya.keisuke@canon.co.jp>, <public-exi-comments@w3.org>
Cc: <youenn.fablet@crf.canon.fr>, <fujisawa.jun@canon.co.jp>
Message-ID: <EB607A77151D455AA7D110939EE3EAAE@cataroimo>

Hi Tamiya-san,

This response attempts to address one of the two issues you brought up
in  your comment with regards to XML declaraion.  Below we provide the
rationale on which we based our decision not to provide direct support for
XML "version" pseudo-attribute in EXI format. Another response is planned
for addressing "standalone", which we consider is related to, yet independent
of XML "version" discussion that we describe here.

The version of XML that occurs in the XML declaration is for indicating the
slightly different syntax rules implied by each XML version (i.e. XML 1.0
vs XML 1.1 as of this writing).

EXI format is a representation of XML Information Set [1]. We are aware that
the Document Information Item [2] in Infoset provides a "version" property
that corresponds to the XML version. However, the value of that property does
not imply different semantics that need to be captured at the Infoset level.
These are the reasons that explain why EXI is, as well as should, be agnostic
about the version of XML.

In some anticipated scenarios of EXI use, application programs are concerned
only of the infoset, with no involvement of serialization in XML at any point
of the processing and communication chains. In such applications, "version"
property of Document Information Item would not provide any benefits.

Also, in applications where serialization of infoset in XML is involved in
conjunction with EXI along the way of computing chains, the preservation of
the original XML version is rarely concerned. This is because the programs
that consume the data are again are, more often than not, only concerned of
the infoset, not particularly of the subtle discrepancy of the XML 1.x syntax.
The recent publication of XML 1.0 5th edition [3] in a sense has made this
argument more indisputable, given that the one single most outstanding
discrepancy that was present between the XML 1.0 and 1.1, the repertoire of
characters, is now essentially dissolved.

Yet, we understand that there are use cases where the use of a particular
version of XML is required when serializing infoset into XML. On such
occasions, it is the program that subsequently consumes the serialized XML
that calls for a particular XML version. We consider XML version as the
artifact of XML serialization, and therefore is the function of XML
serializer implementations, instead of being something that has to be
inherited from the source XML if any that was fed into the computing chain
as an input.

As described above, we do not foresee critical issues to be caused by
not providing the placeholder field in EXI format for carrying text XML version
numbers. On the other hand, there could be substantive cost if EXI supports
XML version numbers in the grammar system, because doing so would
cause every instance of EXI streams to grow slightly in size even when the
XML version value is absent. One of the major uses of EXI, that is, frequent
exchange of tiny documents could suffer from this, because it is typical that
such tiny documents are designed very carefully to pinch on bits to maximize
efficiency. Considering those balances, we decided to forgo the "version"
property of Document Information Item of Infoset.

[1] http://www.w3.org/TR/xml-infoset/
[2] http://www.w3.org/TR/xml-infoset/#infoitem.document
[3] http://www.w3.org/TR/2008/REC-xml-20081126/

-taki


-----Original Message-----
From: public-exi-comments-request@w3.org [mailto:public-exi-comments-request@w3.org] On Behalf Of TAMIYA Keisuke
Sent: Thursday, November 06, 2008 10:22 PM
To: public-exi-comments@w3.org
Cc: youenn.fablet@crf.canon.fr; fujisawa.jun@canon.co.jp
Subject: Question about EXI Draft - XML declaraion


Dear W3C EXI WG members,

I have a question about this draft specification.

EXI does not support the XML declaration - character encoding scheme,
standalone, version. (ref. B.1).
But why does not it support the XML declaration?
I think "character encoding scheme" is not necessary, but I cannot
understand why the "standalone", "version" is not suppoerted.

Regards,
Keisuke Tamiya (tamiya.keisuke@canon.co.jp)
Received on Wednesday, 7 January 2009 20:13:00 GMT

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