Re: Formulate erratum text on versioning for the web architecture document

Hello Noah,

Thanks very much for the comments. Addressing only the current action  
for now. More on the general issue later:

On Feb 17, 2009, at 4:42 PM, ext noah_mendelsohn@us.ibm.com wrote:

> John proposes:
>
>> I believe that the best practice is still correct and important -  
>> data
>> format specifications should provide a mechanism (where that  
>> mechanism
>> might simply be "use XML namespaces") allowing instances to indicate
>> version information. Authors will likely not know whether they will
>> later have to create a new, incompatible version of a format a  
>> priori,
>> but should likely assume that they will.
>
> Well, I still respectfully disagree.  This suggests that a big  
> subset of
> the programming languages we use are poorly designed because they  
> don't
> invite us to say things like:
>
>        <?php PHPVersion="4.1"  ...  ?>
>
> or to put Java version="2.0"  in our Java source files.

I was addressing specifically the documentation produced in AWWW  
Section 4 [1], which states:

> "A data format specification (for example, for XHTML, RDF/XML, SMIL,  
> XLink, CSS, and PNG) embodies an agreement on the correct  
> interpretation of representation data."

Section 4.2 on versioning and extensibility thus seems intended to  
relate specifically to "data format specifications" and to a specified  
agreement regarding representation data.

As such, I don't feel that this text casts aspersions on languages  
such as PHP (which as far as I know has no language specification) or  
Java. I am not sure that they have the same needs with respect to  
"agreement on the correct interpretation of representation data". I do  
find your comments, however, to be instructive. I'm just not sure how  
to best use them yet in this specific case.

>  I gave my reasons
> in the blog posting, and I won't repeat them here.
>
>> I would suggest, however, that perhaps an additional best practice
>> might be warranted, along the lines of Noah's suggestion in [3]:
>>
>> "If a language, or data format, changes in incompatible ways, a new
>> version identifier should be assigned to the updated data format, and
>> allowed in document instances."
>
> Thank you.  I do think that bit is worth saying.  Overall, I might  
> go with
> something like this:
>
> "In cases where the same instance document has incompatible meanings  
> per
> two or more versions of the language specification, provision MUST  
> be made
> for indicating the version(s) used to encode each instance.  Use of
> explicit version identifiers in other languages is optional, and in  
> some
> cases such explict identifiers can actually inhibit the adoption of  
> new
> language versions, or can inhibit interoperability between systems
> implementing differing versions of the language."

Are you saying that a new version identifier should not always be  
minted just because a new version of the language has been? That at  
least is the intent I had in writing the additional best practice text.

But I would like to separate the idea of creating a mechanism for  
allowing version indications, from the practice of assigning and using  
new version indicators.

>
> ...or words to that effect.
>
> As an example of that last admonition, one can argue that XML 1.1  
> might
> have been deployed much more successfully if no version attribute were
> provided in the XML declaration.

The point I have been trying to make is that this issue doesn't seem  
to be about whether a version attribute is _provided_ in the format  
specification; it is about whether a new version identifier is created  
when a new version of a language is created.

>  I don't believe it's the case that the
> same document ever had two different legal meanings in XML 1.0 and XML
> 1.1;  it's just that some documents are legal in one version and some
> legal in the other.  XML 1.0 processors would have rejected content  
> using
> new XML 1.1 characters just as surely (if not just as early) if no  
> version
> identifier were provided.  The ID is really just a cross check or  
> early
> warning in such cases.  The only time it's really crucial is if the  
> same
> document can mean different things as the specification changes.

I don't think this is a problem caused merely by the existence of a  
'version' attribute.

Regards,

- johnk

[1] http://www.w3.org/TR/webarch/#formats

Received on Tuesday, 17 February 2009 22:39:12 UTC