McIntyre-san
In generally speaking, Conneg-tag has following problems;
(1) Difficult to analyze
G3FAX capabilities can be encoded to Conneg-tag, but it is difficult to
convert opposite direction.
It is difficult to analyze Conneg-tag by a G3FAX based IFAX system.
(2) Redundancy of expression
There is no limit of redundant and complicated expression in Conneg-tag.
G3FAX capabilities can be expressed in thousands Byte using Conneg-tag format,
while it can be expressed within 108bit in DIS signal of T.30.
(3) Standard
Conneg-tag is standardized as RFC2879,
while DIS signal of T.30 is not standardized in IETF for fax capabilities
expression.
DIS signal of T.30 is well defined and has a proof of inter connectiveties
between fax manufacturers,
but Conneg-tag does not.
We need some Internet Draft for standardization of fax capabilities such as
DIS MIME type.
Following is just analogy;
English can be translated in Esperanto which is synthesized language as a
perfect language and defined in RFC.
American people want to use English to communicate each other, but do not
want to use Esperanto.
At 11:44 00/11/22 -0800, McIntyre, Lloyd wrote:
>Paul,
>The note from Graham Klyne, see below, addresses the conneg combinatory
>explosion issue raised in item 4 of your meeting summary.
>>Lloyd
>> > -----Original Message-----
> > From: pmoore at peerless.com [mailto:pmoore at peerless.com]
> > Sent: Monday, November 20, 2000 8:56 AM
> > To: ifx at pwg.org> > Subject: IFX> Second IPP fax meeting
> >
> >
>---snip---
> >
> > 4. We discussed conneg. Somebody with actual implementation
> > experience pointed
> > out that it was very unwieldy - you get a combinatory
> > explosion in most
> > non-trivial cases. Still nobody has come up with a better idea.
> >
>---snip---
>>>-----Original Message-----
>From: Graham Klyne [mailto:GK at Dial.pipex.com]
>Sent: Tuesday, November 21, 2000 1:35 PM
>To: McIntyre, Lloyd
>Subject: Re: FW: IFX> Second IPP fax meeting
>>>At 10:34 AM 11/21/00 -0800, you wrote:
> >Graham,
> >Any feedback on item 4 below?
>>Lloyd,
>>Yes...
>>Combinatorial explosion can be an issue; for most expressions, I think it
>is manageable in all but the most memory-constrained environments. I think
>the fax examples are about as complex as an expression should get. To
>minimize the combinatorial effect, my suggestions are:
>>(a) don't attempt to expand or simplify an expression until actually trying
>to match another,
>>(b) use a generate/test strategy that discards unmatched options before
>proceeding to generate the next. In some cases, a whole branch of the
>expression tree can be discarded without further expansion. In any case,
>only possible matches are stored.
>>(c) try to keep simple alternatives (set expressions) together; e.g.
>rather than expanding
> (feature=[a,b,c])
>to
> (| (feature=a) (feature=b) (feature=c))
>keep it as a primitive comparison. This will require an extension to the
>simple expression processing logic so that expressions like:
> (& (F=[a,b,c]) (F=[a,c,e] )
>can be reduced to:
> (F=[a,c])
>>>I think it is also possible to perform a degree of "factorization" on the
>feature expressions, so that alternative constructs containing features not
>mentioned elsewhere are kept intact (rather than transformed to disjunctive
>normal form), without changing the ultimate result.
>>>I have been planning to add some of these improvements to my sample code,
>but had never got around to it.
>>>When reducing to disjunctive normal form, the main cause of combinatorial
>explosion is inner disjunctions:
> (& (| (A) (B) (C) )
> (| (D) (E) (F) ) )
>gives rise to:
> (| (& (A) (D) )
> (& (A) (E) )
> (& (A) (F) )
> (& (B) (D) )
> (& (B) (E) )
> (& (B) (F) )
> (& (C) (D) )
> (& (C) (E) )
> (& (C) (F) ) )
>so any heuristic that limits unnecessary expansion of these can reduce the
>combinatorial effects. This factor might be considered in designing the
>construction and combination of feature sets.
>>>#g
>>------------
>Graham Klyne
>(GK at ACM.ORG)
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Toru MAEDA
CANON Inc. OIP Technology Adv. 3
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