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Re: First PS TF meeting

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 12 Nov 2008 12:22:56 -0500
To: Chris Welty <cawelty@gmail.com>
cc: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>
Message-ID: <29837.1226510576@ubuhebe>


> Sorry for the continued delay getting this started - but let's go.  First 
> presentation syntax task force meeting will be this Friday (Nov. 14) at 11AM 
> EST 
> (that's the usual RIF telecon time, but a different day).
> 
> Please let me know if you plan to attend so I can reserve enough zakim ports.

+1   (in the sense of rsvp += Sandro)

  - s

> I'd like to start by reviewing Hassan's comments below.
> 
> -Chris
> 
> 
> 
> Hassan Ait-Kaci wrote:
>  > Hello,
>  >
>  > This is an update on my on-going efforts to produce a working parser and
>  > XML serializer for the BLD Presentation Syntax: Action 564, due on
>  > October 31, 2008 (http://www.w3.org/2005/rules/wg/track/actions/564).
>  >
>  > I had already produced such a thing for the original specs - i.e., before
>  > several changes were made that have had the effect of introducing several
>  > rather nasty ambiguities and context sensitivity, both at the lexical and
>  > syntactic levels - even just for the canonical PS (i.e., even w/o the DTB
>  > shortcuts and Adrian's Abridged PS).
>  >
>  > I have been struggling trying to find workarounds to whatever snags have
>  > popped up whenever I could figure any. However, there still remain some
>  > tricky situations that require our attention (at least so that we produce
>  > specs that are not so uselessly complicated to implement without ad hoc
>  > hacks).
>  >
>  > It would be good that the PS Task Force convene sometime soon to discuss
>  > these issues and how to resolve them.
>  >
>  > Here are some examples of what I have puzzled over (this is non exhaustive
> ):
>  >
>  > 1) Tokenizing the argument of the Prefix and base directives is made
>  >    uselessy complex by not enclosing the IRI in double quotes (viz., it
>  >    forces a lexer to *parse* IRI's - as opposed to just read them off -
>  >    for no purpose whatsoever, making the lexical nature of some characters
>  >    context-sensitive (for example, ':' is used as a delimiter for CURIE's
>  >    but not within IRI's; or, '#' is used as class membership, but not
>  >    within IRI's; etc, ...).
>  >
>  >    A possible workaround is simply to double-quote them in the directives.
>  >
>  > 2) The minus sign ('-') now appears in some identifiers (e.g., ?diffdays =
>  >    External(func:days-from-duration(?diffduration)). This would be no
>  >    problem if we just considered '-' to be part of identifiers like '_',
>  >    but it must also be seen as a literal character in order to recognize
>  >    tokens such as "->" and ":-". While this is not a major hitch, it is
>  >    unnecessary. (Not to mention the fact that '-' is the subtraction
>  >    operator in the APS.)
>  >
>  >    A possible workaround is simply to disallow '-' in identifiers (say,
>  >    using '_' instead) - as is the case in most programming languages.
>  >
>  > 3) The ANGLEBRACKIRI notation can be dealt with declaring '<' and '>' as
>  >    quote chars, but this precludes them from being used as operators or
>  >    punctuation.
>  >
>  > 4) UNITERM's are defined to be either positional or attributed, but not
>  >    both:
>  >
>  >        UNITERM ::= Const '(' (TERM* | (Name '->' TERM)*) ')'
>  >
>  >    This creates an inherently unliftable reduce/reduce syntactic ambiguity
> :
>  >
>  >        =============================
>  >        STATE NUMBER: 54
>  >        =============================
>  >        This state has conflicts:
>  >
>  >        Unresolved R/R conflict: choosing R82	over R84, 	on inpu
> t 'IDENTIFIER'
>  >        Unresolved R/R conflict: choosing R82	over R84, 	on inpu
> t 'CLOSEPAR'
>  >        -----------------------------
>  >        [45] UniTerm --> Const 'OPENPAR' . UniTermBody 'CLOSEPAR'
>  > 	       Preceding states: {22, 51, 95, 120, 127, 148}
>  > 	       Follow set: {'CLOSEPAR'}
>  >        [66] UniTermBody --> . Term_star
>  > 	       Preceding states: {54}
>  >        [67] UniTermBody --> . TermAttribute_star
>  > 	       Preceding states: {54}
>  >        [82] Term_star --> .
>  > 	       Preceding states: {54}
>  > 	       Lookahead set: {'EXTERNAL', 'NUMBER', 'LOCALNAME', 'VARIABLE', 
> 'STRING', 'IDENTIFIER', 'ANGLEBRACKIRI', 'CLOSEPAR', 'OPENMETA', 'COLON'}
>  >        [83] Term_star --> . Term_star Term
>  > 	       Preceding states: {54}
>  >        [84] TermAttribute_star --> .
>  > 	       Preceding states: {54}
>  > 	       Lookahead set: {'IDENTIFIER', 'CLOSEPAR'}
>  >        [85] TermAttribute_star --> . TermAttribute_star TermAttribute
>  > 	       Preceding states: {54}
>  >        -----------------------------
>  >        With UniTermBody, go to state 55
>  >        With Term_star, go to state 56
>  >        With TermAttribute_star, go to state 57
>  >
>  >     A possible workaround is to use modify the rule to:
>  >
>  >        UNITERM ::= Const '(' (TERM | (Name '->' TERM))* ')'
>  >
>  >     (i.e., accepting mixed positional and attributed term bodies), and
>  >     perform a check ex post facto.
>  >
>  > 5) According to http://www.w3.org/TR/rif-bld/#sec-ebnf-condition-language:
>  >
>  >       An IRICONST is the special case of a Const with the symbol
>  >       space rif:iri, again permitting the shortcut forms defined in
>  >       http://www.w3.org/TR/rif-bld/#ref-rif-dtb. One such specialization
>  >       is '"' IRI '"^^' 'rif:iri' from the Const production, where IRI is a
>  >       sequence of Unicode characters that forms an internationalized
>  >       resource identifier as defined by 
> http://www.w3.org/TR/rif-bld/#ref-rfc-3987.
>  >
>  >     However, this definition complicates tokenizing as it becomes
>  >     impossible to distinguish the special case from the general one.
>  >
>  >     A possible workaround is to see an IRICONST as just a fully qualified
>  >     constant; i.e., accepting even not "rif:iri" symbol spaces and
>  >     performing the check ex post fact.
>  >
>  > Again, this is not an exhaustive list of issues. Be those as they may, I
>  > will continue working on trying to produce a working [A]PS parser as my
>  > time permits while on the road (I have been traveling and will be until
>  > Nov. 11).
>  >
>  > It will be good that the PS Task Force discuss and find resolutions to all
>  > such issues.
>  >
>  > Regards,
>  >
>  > -hak
>  > --
>  > Hassan Aït-Kaci  *  ILOG, Inc. - Product Division R&D
>  > http://koala.ilog.fr/wiki/bin/view/Main/HassanAitKaci
>  >
>  >
> 
> -- 
> Dr. Christopher A. Welty                    IBM Watson Research Center
> +1.914.784.7055                             19 Skyline Dr.
> cawelty@gmail.com                           Hawthorne, NY 10532
> http://www.research.ibm.com/people/w/welty
> -- 
> Dr. Christopher A. Welty                    IBM Watson Research Center
> +1.914.784.7055                             19 Skyline Dr.
> cawelty@gmail.com                           Hawthorne, NY 10532
> http://www.research.ibm.com/people/w/welty
Received on Wednesday, 12 November 2008 17:23:19 GMT

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