Subject: [Megaco] Ambiguous definition of auditReturnParameter in v2 ABNF

From: Micael Karlberg <[email-masked]>
Date: Thu, 17 Jul 2003 11:31:34 +0200

Hi,

The 'auditReturnParameter' appears to be ambiguously defined in version 2
of the ABNF.

An example. If the 'auditReturnParameter' contains the following 
sequence of tokens:

   "EB { hobbes }"

i.e.

    EventBufferToken LBRKT pkgdName RBRKT

then it may be an 'auditItem' (see 'indAudeventBufferDescriptor') or an 
'eventBufferDescriptor'

What is the intention here? Should this sequence of tokens be
interpreted as an 'auditItem' or an 'eventBufferDescriptor?

As a parser implementor I need a well defined, unambiguous grammar to
rely on.

The grammar looks like this (a little bit simplified):

  auditReturnParameter        = eventBufferDescriptor / auditItem

  eventBufferDescriptor       = EventBufferToken 
                                [ LBRKT eventSpec *(COMMA eventSpec) RBRKT]

  eventSpec                   = pkgdName  
                                [ LBRKT eventSpecParameter 
                                        *(COMMA eventSpecParameter) RBRKT]

  auditItem                   = indAudterminationAudit 

  indAudterminationAudit      = indAudauditReturnParameter
                                *(COMMA insAudauditReturnParameter)

  indAudauditReturnParameter  = indAudeventBufferDescriptor

  indAudeventBufferDescriptor = EventBufferToken LBRKT indAudeventSpec RBRKT

  indAudeventSpec             = pkgdName 
                                [ LBRKT indAudeventSpecParameter RBRKT ]

Regards,
	/BMK

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From: "Anil Jangam" <[email-masked]>
Date: Thu, 17 Jul 2003 16:52:33 +0530

This particular question has been repeated for a number of times so far.
Even I had the same doubt for which Tom has replied as follows: (Marked with
####>).
I think we need to fix this now.

####> STARTS
----- Original Message -----
From: Tom-PT Taylor
To: 'Anil Jangam' ; Kevin Boyle
Sent: Wednesday, January 22, 2003 10:40 PM
Subject: RE: [Megaco] auditReturnParameter in AmmsReply

I suppose as the guy who concocted this syntax I should answer the question.
You return the auditItem.  That was my shortcut for returning descriptor
name only.

Apparently there is a parsing problem with this syntax, but we never seem to
have taken the step of resolving it.
####> ENDS

---

From: "Anil Jangam" <[email-masked]>
Date: Thu, 17 Jul 2003 16:52:33 +0530

####> STARTS

---

From: Aleksandr Ryabin <[email-masked]>
Date: Thu, 17 Jul 2003 10:01:42 -0400

>Date: Thu, 05 Jun 2003 12:36:31 -0400
>To: Troy Cauble <[email-masked]>, "Jay H Kim" <[email-masked]>,
>    "Anil Jangam" <[email-masked]>, [email-masked]
>From: Aleksandr Ryabin <[email-masked]>
>Subject: Re: [Megaco] EventsToken in auditItem of teminationAudit or
>   empty eventsDescriptor
>
>See "6.3 Empty Descriptor Syntax" in IG.
>http://standard.pictel.com/ftp/avc-site/0305_Gen/H.248_IG.zip
>         Aleks
...

---

From: Aleksandr Ryabin <[email-masked]>
Date: Thu, 17 Jul 2003 10:01:42 -0400

...

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From: Micael Karlberg <[email-masked]>
Date: Fri, 18 Jul 2003 11:21:14 +0200

So, now we have yet another parse conflict regarding 'EventBufferToken'?

We three rules:

1) auditItem                   -> 'EventBufferToken'
2) eventBufferDescriptor       -> 'EventBufferToken' 
                                  [ LBRKT eventSpec *(COMMA eventSpec) RBRKT ]
3) indAudeventBufferDescriptor -> 'EventBufferToken' 
                                  LBRKT indAudeventSpec RBRKT

One conflict between rule 1) and 2) and now another conflict
between rule 2) and 3)

So, depending on the number of tokens after the 'EventBufferToken', we get:
 - Zero        -> auditItem
 - One         -> indAudeventBufferDescriptor
 - Two or more -> eventBufferDescriptor

Is this correct?

Regards,
	/BMK

-- 
Micael Karlberg          Ericsson AB, Älvsjö Sweden
Tel:  +46 8 727 5668     EAB/UHK/KD - OTP Product Development
ECN:  851 5668           Mail: [email-masked]
Fax:  +46 8 727 5775

---

From: Micael Karlberg <[email-masked]>
Date: Fri, 18 Jul 2003 11:21:14 +0200

We three rules:

Is this correct?

Regards,
	/BMK