Subject: Re: [Iptel] comments on rfc2806bis - grammar

From: [email-masked]
Date: Tue, 3 Dec 2002 12:20:45 EST

In a message dated 12/3/2002 10:43:04 AM Eastern Standard Time, 
[email-masked] writes:

> We've had a similar discussion in the SIP WG. ABNF is not sufficient to 
> completely describe all legal (or illegal) patterns. In particular, 
> expressing
> 
> 'at most once, in any order'
> 
> is not easily expressible in ABNF (for more than one item). If you have 
> a suggestion, please offer it. The only way I have found is to enumerate 
> all combinations, which quickly gets ouf of hand, as in
> 
> context isub ext | context ext isub | ext context isub | ...
> 
> with *par sprinkled in between each element. This is probably barely 
> manageable for our current set of known parameters (;phone-context ;isub 
> ;ext), but this will fail if another draft adds another one (say, ;cic).
> 

[MAP] Then why are we using ABNF and spending so much time on it if it is 
"not sufficient"?

If it is a choice between explicitly showing the order or explicitly showing 
that a parameter can occur only once, I would opt for the latter.

I certainly would not expect to see this complication in the ABNF if the only 
purpose is to say that different orders are okay. And, as you say, adding 
another paramter would be a worse mess. In fact, why not specify the order?

I don't have a suggestion, since I think I've lost sight of what it is we're 
trying to do. Based on a number of comments, I think we need to step back and 
re-assess what the purpose of all this is. Richard Stastny had a list of uses 
of the tel:uri as:

-on a web-page
-in SIP messages, ev. with the yu-extensions
-in ENUM NAPTRs, also with the yu extensions and maybe others.

And he noted that all three may have different requirements. (Like I would 
not expect a "local-number" or 911 or visual separators to ever be in a 
NAPTR.)

Are there other uses?

MIke Pierce
Artel

---

From: Henning Schulzrinne <[email-masked]>
Date: Tue, 03 Dec 2002 12:35:56 -0500

> [MAP] Then why are we using ABNF and spending so much time on it if it
> is "not sufficient"?

Because URIs are specified with ABNF :-) Nothing is perfect - lots of 
constraints can't be captured at the BNF level, but that doesn't make 
BNF useless.

> I certainly would not expect to see this complication in the ABNF if the
> only purpose is to say that different orders are okay. And, as you say,
> adding another paramter would be a worse mess. In fact, why not specify
> the order?

I have no objection to specifying a fixed order. It would differ from 
the SIP URI "tradition", but this flexibility seems to add little real 
value. The only real problem is that parameters that we add later need 
to reference all other extension parameters, to maintain that order. I 
guess the 'order number' could be part of the IANA registration.

> Are there other uses?

I'm sure sooner or later H.323 will pick it up, too. It will just take a 
few years :-)

> Artel

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From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 03 Dec 2002 13:12:20 -0500

This is not the opportunity to revisit the way in which we are encoding 
parameters in URIs. To date, the ordering was not fixed, and it was up 
to the semantic text to tell you that you should have only one instance 
of a parameter. Let us stick with that and move on.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
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