Re: Extension/Extensibility examples in W3C Specifications

On Wed, 5 May 2004, Mark Skall wrote:

> > >I think the word *additional* is crucial - an extension which
> > >negates the base specification is not an extension but a change.
> > >Of course, quite what constitutes "negating" is domain dependent.
> >
> >I don't think so, changes make something ambiguous, you can infer
> >different things from the same thing prior and after the change,
> >even though the input remains the same. With an extension you have
> >different things where you naturally infer different things from.
>
> I agree with Jeremy.  When we write specs and include the concept of
> extensions we say something like " the additional feature/function
> cannot contradict or cause the non-conformance to other
> features/functions in the spec."

FWIW, here is what seems like a counter-example from OCP Core protocol
specs that IETF OPES WG is working on:

1.3  Terminology
...
 OCP extension: A specification extending or adjusting this document
   for adaptation of an application protocol (a.k.a., application
   profile, e.g., [I-D.ietf-opes-http]), new OCP functionality (e.g.,
   transport encryption and authentication), and/or new OCP Core
   version.
...

15.1  Extending OCP Core

   OCP extensions MUST NOT change OCP Core message format, as defined by
   ABNF and accompanying normative rules in Section 3.1. The intent of
   this requirement is to allow OCP message viewers, validators, and
   "intermediary" software to at least isolate and decompose any OCP
   message, even a message with unknown to them (i.e., extended)
   semantics.

   OCP extensions are allowed to change normative OCP Core requirements
   for OPES processors and callout servers. However, OCP extensions
   SHOULD NOT make such changes and MUST require on a "MUST"-level that
   such changes are negotiated prior to taking effect. Informally, this
   specification defines compliant OCP agent behavior until changes to
   this specifications (if any) are successfully negotiated.
...


This information is outside of the scope identified in the Subject
line, but I hope you find it useful.

Alex.

Received on Wednesday, 5 May 2004 11:17:07 UTC