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re: revised CGZ proposal

From: Lofton Henderson <lofton@rockynet.com>
Date: Thu, 04 Dec 2008 11:56:05 -0700
Message-Id: <5.1.0.14.2.20081204115014.02a35b10@localhost>
To: WebCGM WG <public-webcgm-wg@w3.org>

Thanks for the comments, Don.

Per today's telecon, Part 1 is closed and agreed.

Part 2, the "lurking question", is what we're seeking comment on.  You 
opined, "...a WebCGM 2.1 viewer should handle legacy WebCGM gziped 
files".  To be precise, the requirement would be phrased for 2.1 viewers 
that claim 1.0 and/or 2.0 backward compatibility.  I.e., if they claim 
conformant handling of 1.0 and/or 2.0 metafiles, then they shall correctly 
handle gzip'd versions of such.

I would imagine this includes all 2.1 viewers in practice, but the wording 
needs to be careful, because a viewer can in theory be 2.1 conformant but 
not 1.0 conformant.

(FWIW, I agree that it is a sensible and practical requirement.)

-Lofton.

At 11:21 AM 12/4/2008 -0600, Don wrote:

>Lofton,
>
>  >  All --
>
>  >  I'm going to propose a slightly different resolution than what is in the
>  >  previous (below-attached) thread.  Approval of this change will be on the
>  >  next WG telecon agenda (04-dec).
>
>  >  Part 1:  basic resolution
>  >  ==========
>
>  >  Basically, to accommodate dissatisfaction with potential bending the
>  >  CGM:1999 Rules for Profiles, we will instead make gzip support a 
> Chapter 7
>  >  viewer requirement, that WebCGM 2.1 viewers properly handle
>  >  gzip-compressed Binary-encoded WebCGM 2.1 content.
>
>  >  The proposal:
>
>  >  1.) remove the "Other:..." gzip requirement from T.13.1 in Chapter 6;
>  >  2.) Add to the end of @@7.1:  "WebCGM 2.1 viewers, both static and
>  >  dynamic, must correctly handle valid WebCGM 2.1 Binary-encoded metafiles
>  >  that are gzip-compressed."
>
>  >  That, I believe, captures the sense of recent discussions.  Comments on
>  >  that part of it?
>
>I agree.
>
>  >  Part 2:  a lurking question
>  >  ===========
>
>  >  I will point out in advance that this revision leaves open a question
>  >  about WebCGM 2.1 viewers and gzip'd 2.0 or 1.0 content.  If you look at
>  >  Ch.7's deprecation and obsoletion wording, for example, you will see that
>  >  we don't require that a conforming 2.1 viewer be a conforming 2.0 viewer
>  >  (nor 1.0).  But 2.1 viewers can optionally feature 2.0/1.0 conformance --
>  >  i.e., correct handling of 2.0 and 1.0 metafiles per the 2.0/1.0
>  >  conformance rules.  In fact, I would guess that almost all are built that
>  >  way.
>
>  >  So the question:  do we want to apply the 2.1 viewer gzip requirements to
>  >  older content (2.0/1.0), for those 2.1 viewers that claim backward
>  >  compatibility for 2.0/1.0?  I.e., something like "In addition, 2.1 
> viewers
>  >  that correctly handle valid 2.0 or 1.0 content per the conformance
>  >  requirements of those (2.0 or 1.0) WebCGM versions shall correctly handle
>  >  such metafiles when they are gzip compressed."
>
>  >  Please comment on that refinement, pro or con.  What do people want?
>
>I think that a WebCGM 2.1 viewer should handle legacy WebCGM gziped files.
>Since the viewer needs to un-gzip to determine the profile anyway, the viewer
>might as well go ahead and handle the un-gzipped contents.
>
>Don.
>
>  >  (In parallel, Lofton has an action item to contact Dick Puk at SC24 about
>  >  processing a corrigendum or addendum to ISO 8632, that would add
>  >  gzip-compressed Binary, at least, to the valid encoding/content types of
>  >  ISO 8632).
>
>  >  -Lofton.
>
>  >  At 02:54 PM 11/12/2008 -0800, David Cruikshank wrote:
>  >  I like this solution.  As long as I'm using a 2.1 viewer, it doesn't
>  >  prevent me from using zipped cgm files in my database of graphics.
>
>  >  Dave
>
>  >  On Wed, Nov 12, 2008 at 12:13 PM, Lofton Henderson <lofton@rockynet.com>
>  >  wrote:
>  >  All --
>
>  >  Having read preferences and concerns in this thread, and following on 
> from
>  >  the discussion that happened this morning in the TC's telecon, IMHO this
>  >  is the right way to handle the CGZ questions that Benoit raised...
>
>  >  1.) completely clarify in 2.1 text that gzip'd binary CGM (content) is a
>  >  valid conformance "Class of Product" for WebCGM 2.1, and that all 2.1
>  >  interpreters must handle it.
>
>  >  2.) say *nothing* in the 2.1 spec about 1.0, 2.0, or other profiles.  (In
>  >  other words, use of gzip'd binary CGM in other contexts is by private
>  >  agreement about archival and transport, and there will be no suggestion,
>  >  MUST, SHOULD, or whatever -- neither implied nor explicit -- in the 2.1
>  >  spec about it.)
>
>  >  This seemed agreeable to everyone this morning, and seems to resolve
>  >  concerns about creating retroactive, even implied, requirements about
>  >  already deployed systems for 1.0, 2.0, and other profiles.
>
>  >  Are there any objections to this resolution?
>
>  >  Other comments?
>
>  >  Regards,
>  >  -Lofton.
>
>  >
>
>  >  At 03:30 AM 11/12/2008 -0500, Weidenbrueck, Dieter wrote:
>  >  Dave,
>  >
>  >  this is pretty much how I feel about this as well.
>  >
>  >  The challenge is, if we do #1 inside the WebCGM 2.1 profile, then
>  >
>  >  - an unzipped PIP or GREXCHANGE 2.6 file is compliant to the respective
>  >  profile
>  >  - a zipped PIP or GREXCHANGE 2.6 file is compliant to ...what??
>  >
>  >  If a compliant interpreter can read a GREX 2.6 file in zipped form, is
>  >  this a compliant behavior? If it can't, is the interpreter not compliant
>  >  any more?
>  >
>  >  if we set up a rule within a specific profile, it will be valid only for
>  >  that profile. In fact, there is an open question that I can't answer here
>  >  on the road, which is:
>  >  Every CGM file compliant to a profile must be a legal ISO8632 CGM. Is a
>  >  zipped CGM a legal ISO8632 CGM? If you read it following the ISO 
> standard,
>  >  you will have to reject the file as non-CGM after the first bytes. Or, in
>  >  other words, isit legal to define zip compression inside a profile, or
>  >  does it have to be a separate encoding?
>  >
>  >  Dieter
>  >  From: public-webcgm-wg-request@w3.org
>  >  [mailto:public-webcgm-wg-request@w3.org] On Behalf Of David Cruikshank
>  >  Sent: Dienstag, 11. November 2008 18:31
>  >  To: Lofton Henderson
>  >  Cc: WebCGM WG
>  >  Subject: Re: CGZ files
>  >
>  >  >From a user standpoint, I would lean towards option 1.  That is not
>  >  requiring that cgz only be used with 2.1, but using informative language
>  >  to indicate that cgz files might contain cgm files from previous 
> profiles.
>  >  My reasoning is based on a question I get all the time from people in the
>  >  industry.  "Do I have to open up every CGM file and change the ProfileEd
>  >  every time the industry profile rolls."  Creating a zip content for a CGM
>  >  file can be done without ever touching the file with a CGM tool and I can
>  >  see where an application might take advantage of the cgz file just by
>  >  converting it's whole database.
>
>  >  A second question....Does anyone really thing a viewing application is
>  >  going to access a cgz file, unzip it, and the if the ProfileEd is not 
> 2.1,
>  >  reject the fiile and not display it?
>
>  >  thx...Dave
>
>  >  On Mon, Nov 10, 2008 at 12:34 PM, Lofton Henderson <lofton@rockynet.com>
>  >  wrote:  Hi All,
>
>  >  As I'm working on the summary of LC comments, I realize that we haven't
>  >  completely put the CGZ question to rest yet -- there are loose 
> ends.  (See
>  >  my summary below attached.)  Benoit mentioned this also at the end of the
>  >  WG telecon.
>
>  >  About 2.1:  I think we agree that it is a valid content type for 2.1,
>  >  right?  I.e., gzip-compressed binary CGM content is a conforming Class of
>  >  Product for 2.1.  And 2.1 interpreters must handle it.  So we can clarify
>  >  the wording about 2.1 in the 2.1 spec if anyone thinks it is unclear.
>
>  >  About 1.0 & 2.0:  I sense that people want to be able to exchange
>  >  gzip-compressed 1.0 and 2.0 as well.  Correct?
>
>  >  So what are the options:
>
>  >  1.) We could put a non-normative note in 2.1, acknowledging that
>  >  gzip-compressed binary is not conforming 1.0/2.0 content strictly
>  >  speaking, but that it is a useful and used technique, and recommending
>  >  that interpreters should be prepared to handle it.  (And they might
>  >  encounter it in the context of *any* profile of CGM.)
>
>  >  2.) We could process errata for 1.0 & 2.0, making it a formal 
> requirement.
>  >  (This would be a *substantive* errata.)
>
>  >  3.) Other.  E.g. something along the lines of the "storage/transport
>  >  variant outside of CGM".  My question about this option would be:  how
>  >  exactly would such a perspective be reflected in the 2.1 text?  (Is this
>  >  option essentially the same as #1?)
>
>  >  Regards,  -Lofton.
>
>  >
>
>  >
>
>  >
>
>  >
>
>  >
>
>  >
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>  >
>
>  >
>
>  >  At 08:59 AM 10/21/2008 -0600, Lofton Henderson wrote:
>
>  >  At 12:50 PM 10/20/2008 -0400, Weidenbrueck, Dieter wrote:  [...]  I agree
>  >  with your analysis.
>
>  >  One additional question:  Would it make sense to establish cgz as an
>  >  additional encoding (or  something similar) to make it available to other
>  >  profiles?
>
>  >
>  >  It is an interesting idea, and I hear that people would like to be 
> able to
>  >  do it.
>
>  >  "..establish as an additional encoding.." -- That approach would most
>  >  sensibly involve working a corrigendum to CGM:1999 through ISO.  This
>  >  would not be hard, process-wise.  But on the other hand, CGZ would be a
>  >  somewhat different type of encoding than Binary Encoding or Clear Text
>  >  Encoding.  (It is binary-encoded, then compressed as a whole -- not 
> really
>  >  the same sort of thing as the other encodings, IMHO.)  I'm not  thinking
>  >  about WebCGM 1.0 per se, but other profiles building on ISO 8632 might
>  >  want to use zipping as well.
>
>  >
>  >  Yes, there does seem to be a use case, as I gather from you and from 
> Don.
>  >  I guess in general I find it a shame to restrict usage of zipping to
>  >  WebCGM 2.1 only, and I would like to find a way to be able to use
>  >  compression with any variant of CGM. Probably this could be declared 
> as  a
>  >  kind of a storage/transportation variant outside of CGM?
>
>  >
>  >  We should be clear about the current situation.  It does not prohibit the
>  >  use of CGZ compression for WebCGM 1.0 instances.  But it isn't supported
>  >  it as a conformance scenario for 1.0 either, i.e., gzip-compressed CGM is
>  >  not a conformance "Class of Product", and handling gzip-compressed CGM is
>  >  not a requirement for the viewer "Class of Product".  (And 1.0 would in
>  >  fact prohibit it, if it were claimed that the compressed instance is 
> valid
>  >  WebCGM 1.0).
>
>  >  What I mean is this... If "BE21" (BE10) is a valid WebCGM 2.1 (1.0) 
> binary
>  >  metafile, CGZ21 (CGZ10) is a gzip-encoded valid BE21 (BE10) metafile, V21
>  >  (V10) is a conforming 2.1 (1.0) viewer, and Z is a standalone
>  >  gzip-decompressor, then...
>
>  >  Valid WebCGM 2.1 scenario:  ...--> CGZ21 --> [V21]
>
>  >  Valid WebCGM 1.0 scenario:  ...-->CGZ10 ---> [Z] --> BE10 --> [V10]
>
>  >  That is, nothing prevents gzip compression of WebCGM 1.0 metafiles.  But
>  >  it (CGZ10) has no standing as a valid content type for a V10 viewer
>  >  according to the WebCGM 2.1 spec's conformance section.  (Note that the
>  >  V21 viewer implicitly or logically integrates the process "Z", because of
>  >  the conformance specifications of WebCGM 2.1).
>
>  >  This is kind of like what Dieter says -- that it is handled as part 
> of the
>  >  transport process, outside of the specifications of the WebCGM 1.0
>  >  specification.
>
>  >  So ... where do we go from here?  Should we put something (informative)
>  >  into 2.1, pointing out that the conforming 2.1 scenario can 
> essentially be
>  >  achieved also with 1.0 metafiles, except the compressed content CGZ10 is
>  >  not a conforming1.0 "class of product", and therefore must be 
> decompressed
>  >  into a valid BE10 metafile before it is a conforming input to a V10 
> viewer
>  >  process?
>
>  >  Should we process errata for WebCGM 1.0 and WebCGM 2.0?  (Difficult,
>  >  because can be argued as a substantive/technical change, and OASIS 
> process
>  >  prohibits such in Errata.)
>
>  >  Thoughts?
>
>  >  Cheers,
>  >  -Lofton.  -----Original Message-----  From:
>  >  public-webcgm-wg-request@w3.org  [mailto:public-webcgm-wg-request@w3.org]
>  >  On Behalf Of Lofton Henderson  Sent: Montag, 20. Oktober 2008 12:06  To:
>  >  Bezaire, Benoit; WebCGM WG  Subject: RE: CGZ files
>
>  >
>
>  >
>
>  >
>
>  >
>
>  >
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>  >
>
>  >
>
>  >
>
>  >  Benoit,
>
>  >  Oops, my message crossed with yours.
>
>  >  In short:  I agree that this is a conformance requirement for 
> WebCGM  2.1,
>  >  specifically that 2.1 viewers must handle gzip-compressed 2.1  instances,
>  >  and that valid 2.1 instances included plain Binary Encoding  as well as
>  >  gzip-compressedinstances of binary-encoded 2.1 metafiles.
>
>  >  Long analysis:  see my other just-sent message.
>
>  >  -Lofton.
>
>  >  At 11:23 AM 10/20/2008 -0400, Bezaire, Benoit wrote:
>
>  >  >I see your point, however...  >>We have customers using WebCGM 1.0
>  >  "compliant" tools (IsoDraw/IsoView  >v6 for example). Now, these 
> customers
>  >  could get a WebCGM 1.0 .cgz and  >those "compliant" applications would
>  >  reject them. That's not very  >user-friendly.  >>Maybe it's better to do
>  >  this as a WebCGM 2.1 feature.  >>Benoit.  >>-----Original Message-----
>  >  >From: Don L. [mailto:dlarson@cgmlarson.com]  >Sent: Friday, October 17,
>  >  2008 6:59 PM  >To: Bezaire, Benoit  >Cc: WebCGM WG  >Subject: re: CGZ
>  >  files  >>Benoit  >>> Hi  All,  >>>> I find the draft  underspecified 
> about
>  >  compressed CGM files. More  >>specifically, we would like to  know what
>  >  kind of CGM files may be  >>compressed?  >>>> Version1 to  4?  >> Can I
>  >  compress a  WebCGM 1.0 CGM file for example?  >>>> Is this a WebCGM 2.1
>  >  conformance feature for viewer and authoring  >tools?  >> Or is this 
> a new
>  >  WebCGM  2.1 (and only 2.1) 'encoding scheme' ...  >>for  >>>lack  of a
>  >  better  word?  >>I think 'encoding scheme' is a better characterization.
>  >  The text for  >this feature in the webcgm 2.1 spec was extracted from the
>  >  SVG spec.  >>My thinking is that this is a viewer conformance issue and a
>  >  WebCGM 2.1  >viewer should be able to open a file with a .cgz extension
>  >  and know  >that it needa to decode this file according to the gzip spec.
>  >  with the  >assumption that results will be a file that conforms to the
>  >  WebCGM  >profile (any version e.g.  >1.0 , 2.x).  >>Don.  >>> Thanks.  >>
>  >  Benoit.
>
>  >
>
>  >
Received on Thursday, 4 December 2008 18:56:56 GMT

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