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Re: draft-ietf-http-feature-reg-01.txt

From: Graham Klyne <GK@acm.org>
Date: Thu, 10 Jul 1997 16:29:27 +0100
Message-Id: <>
To: Koen Holtman <koen@win.tue.nl>
Cc: http-wg@cuckoo.hpl.hp.com
X-Mailing-List: <http-wg@cuckoo.hpl.hp.com> archive/latest/3718

A couple of comments regarding your feature registration draft...

* Section 3.6, item (3):

In conflict with section 2.2 final paragraph, this item does seem to place
prior restrictions on the things can be identified by a feature tag.

Specifically, the wording suggests the range of a feature value must be a
scalar type (enumeration, number range, etc.).  Compound values seem to be
excluded; e.g. sets (multiple choices), cartesian products
(multidimensional values).

Consider an example of a (hypothetical) map server:  one might wish to
request a map covering a specified rectangular(-ish) area (4 real numeric
values) OR including all of a designated set of counties, with a specified
mapping resolution and containing a minimum specific set of mapping features.

[As an aside:  it occurs to me that, in HTTP transfers, the resource
identifier (URN, URL or whatever) might be considered just another
dimension of the negotiation!]

* Section 3.8:

(A) In "Summary of the indicated dimension of negotiation", I am
uncomfortable with your use of the term 'dimension' in this context.  I
think what you are describing is the range of values associated with a

Underlying this comment is my feeling that I don't think sufficient
distinction is drawn between identification of a dimension of negotiation
(the feature tag) and the values which are associated with that dimension
(feature values?).

(B) I feel your list of "Result in the indicated dimension of negotiation"
is rather arbitrary.  Why separate items (1) and (2)?  Similarly (3) and
(4) in that they both represent a choice from an enumeration of values.  I
would suggest:

(1) A yes/no choice
(2) A choice of one value from a finite enumeration of (possibly numeric)
(3) A choice of multiple values from a finite enumeration of values (powerset)
(4) A value selected from a finite or infinite range of some scalar type
(integer, real)
(5) A compound value (e.g. MIME Content-type, range of numeric values)

[I also note that these values relate to a specific message which is
transferred: the feature negotiation mechanism would have to deal with
multiple values for any of these value range types.]


Graham Klyne
Received on Thursday, 10 July 1997 08:34:19 UTC

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