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Re: discussion of LC comments on Extensions

From: Mark Skall <mark.skall@nist.gov>
Date: Mon, 28 Apr 2003 14:13:12 -0400
Message-Id: <>
To: Lofton Henderson <lofton@rockynet.com>
Cc: www-qa@w3.org

My point was the following.  You responded to the point that the new 
chapter will have a DOV caution by saying that you disagree that we should 
tone it down because "extensibility is #1 on my interoperability list of 
evils."  The DOV caution (which I guess is the "toning down") applies to 
DOVs in general, not extensibility which is just one of the many DOVs.

10:54 AM 4/28/2003 -0600, Lofton Henderson wrote:
>[switching thread to www-qa....]
>At 10:59 AM 4/28/03 -0400, Mark Skall wrote:
>>>>The new Concept chapter will have a DoV caution and we agreed(?) that 
>>>>each DoV would have a simple caution statement.
>>>I have made an alternate proposal, which has been linked from the issue 
>>>list for some time:
>>>I disagree that we should "tone it down" -- extensibility is #1 on my 
>>>interoperability list of evils.
>>Extensibility does not equal DOV.  DOV has to do with variability.  Every 
>>technique for variability does not "extend" the standard.  Subsetting, 
>>for example, does not extend.  rather it organizes things differently
>Hmmm, I'm not quite sure that I understand your point.  Extensibility is 
>one of the (current) 8 DoV, and has been such since June 2002.  From "4. 
>dimensions of variability
>the ways in which different products that are conformant to a 
>specification may vary among themselves. In this Specification Guidelines 
>document, the dimensions of variability are used to help organize, 
>classify and assess the conformance characteristics of W3C specifications
>Extensibility certainly fits as one of the ways in which conformant 
>products may vary amongst themselves.
>My original point was that, while acknowledging the reasons for which 
>specs allow extensibility, we should also keep strong caveats about the 
>consequences.  In my (direct) experience, there have been few cases 
>(none?) in which there is not some interoperability downside, regardless 
>of how well justified the use of extensibility might be.  If someone were 
>to offer an example (no interop downside), it would be interesting to include.
>In the balance, it may indeed be that the benefit of extensibility exceeds 
>the cost.

Mark Skall
Chief, Software Diagnostics and Conformance Testing Division
Information Technology Laboratory
National Institute of Standards and Technology (NIST)
100 Bureau Drive, Stop 8970
Gaithersburg, MD 20899-8970

Voice: 301-975-3262
Fax:   301-590-9174
Email: skall@nist.gov
Received on Monday, 28 April 2003 14:18:21 UTC

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