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Re: Media types and versioning

From: Jan Algermissen <algermissen1971@mac.com>
Date: Tue, 22 May 2007 21:57:35 +0200
Message-Id: <2991B958-DA38-4520-962C-4E1C1F694F9A@mac.com>
Cc: Mark Baker <distobj@acm.org>, David Orchard <dorchard@bea.com>, Marc de Graauw <marc@marcdegraauw.com>, mark@coactus.com, Marc de Graauw <mdegraau@xs4all.nl>, www-tag@w3.org
To: noah_mendelsohn@us.ibm.com

On 22.05.2007, at 19:06, noah_mendelsohn@us.ibm.com wrote:

> Mark Baker writes:
>> I'm ok with the second part of that, but if a new version is
>> compatible, then a new media type shouldn't be required.
> Which begs the question, what do you mean by compatible?

This could be rephrased to "what are the allowed variations between  
two versions
of a format if they are to remain the same media type?".

Has that ever been thought through?


> Almost surely, a
> new version of a language will introduce both new syntax and  
> corresponding
> new information conveyed by that syntax.  So, in that sense, there's
> almost always some incompatibility when new constructs are used.
> Sometimes the new information is in some sense orthogonal to the old,
> allowing one to ask separately which pieces of the content are
> "understood".  Sometimes, the new rules change the implications of  
> the old
> fields.   For example, if the old version says that case doesn't  
> matter
> for a field, and the new version of the language says that case  
> matters,
> then even documents that were legal in the old language may be  
> taken to
> convey information that might not have been intentional when the  
> document
> was authored.   Even in the simple case where the new content is
> completely orthogonal syntactically and semantically, there is the
> question of whether users consider it OK to to ignore if it's not
> understood.
> For reaons like these, I don't think using the word "compatible"  
> without
> explanation or qualification is appropriate.  I do agree that for some
> families of languages, one can define useful notion of  
> compatibility that
> make it appropriate to consider using a single media type for all  
> of the
> versions.  I don't agree that those styles of language evolution are
> always what people want.
> --------------------------------------
> Noah Mendelsohn
> IBM Corporation
> One Rogers Street
> Cambridge, MA 02142
> 1-617-693-4036
> --------------------------------------
> "Mark Baker" <distobj@acm.org>
> Sent by: mark@coactus.com
> 05/18/2007 08:04 AM
>         To:     "David Orchard" <dorchard@bea.com>
>         cc:     noah_mendelsohn@us.ibm.com, "Marc de Graauw"
> <marc@marcdegraauw.com>, "Marc de Graauw" <mdegraau@xs4all.nl>,
> www-tag@w3.org
>         Subject:        Re: Media types and versioning
> On 5/17/07, David Orchard <dorchard@bea.com> wrote:
>> What about incorporating a version # in the media type?
>> Say application/soap+1dot2+xml, etc.
> That's fine.  On the ietf-types list, I think I've recommended
> something similar for at least one format which made backwards
> incompatible changes.
>> Then say in the media type definition that by definition any minor
>> version change is compatible, and any incompatible change will be
>> accompanied by a major version change.
> I'm ok with the second part of that, but if a new version is
> compatible, then a new media type shouldn't be required.
> Mark.
Received on Tuesday, 22 May 2007 19:58:30 UTC

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