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RE: CGZ files

From: Weidenbrueck, Dieter <dweidenbrueck@ptc.com>
Date: Tue, 21 Oct 2008 17:39:11 -0400
Message-ID: <1A56AD0206CE2B4788D0A10F7B08FD8F05D5EE94@HQ-MAIL4.ptcnet.ptc.com>
To: "Lofton Henderson" <lofton@rockynet.com>, "WebCGM WG" <public-webcgm-wg@w3.org>

Lofton,

Following your conclusions:

>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
conforming 1.0
>"class of product", and therefore must be decompressed into a valid
BE10 metafile 
>before it is a conforming input to a V10 viewer process? 

So that raises a question for me:
If we agree that zip compression is more like a "transport feature"
(like ftp compression btw), and if we agree that it is legal to zip a
1.0 file and decompress it before a v1.0 viewer can read it, then
Why do we add zip compression to WebCGM at all? Why don't we define a
pure viewer feature like many others to handle zip compression?

For example, we expect a viewer to download files from a server using
the usual protocols, however, that protocol (e.g. http) is not part of
WebCGM itself.
Could we possibly simply distinguish between viewers that support zipped
CGMs, no matter which version and profile, and viewers that don't?

Supporting the OBJECT tag of HTML is not a part of WebCGM at all, still
the viewer needs to support it.

I guess I am not sure where to put this, perhaps somebody has a good
idea.

Dieter
-----Original Message-----
From: public-webcgm-wg-request@w3.org
[mailto:public-webcgm-wg-request@w3.org] On Behalf Of Lofton Henderson
Sent: Dienstag, 21. Oktober 2008 11:00
To: WebCGM WG
Subject: RE: CGZ files


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 conforming 1.0 "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
>
>
>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-compressed instances 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 Tuesday, 21 October 2008 21:39:51 GMT

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