Re: draft-ietf-http-feature-reg-01.txt
Graham Klyne (GK@acm.org)
Thu, 10 Jul 1997 16:29:27 +0100
Koen,
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
dimension.
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)
values
(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.]
GK.
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Graham Klyne
GK@ACM.ORG