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Re: Problem with RIF-Core specification [was Re: Urgent: Issue with RIF-Core EBNF Grammar?]

From: Jos de Bruijn <jos.debruijn@gmail.com>
Date: Wed, 12 May 2010 12:32:35 +0200
Message-ID: <AANLkTilB9Frwx4UhJ9OxnVPJqz1-QJHjUaVramCEC9L2@mail.gmail.com>
To: RIF <public-rif-wg@w3.org>
[2] http://www.w3.org/2005/rules/wiki/Core#Formulas_of_RIF-Core

On Wed, May 12, 2010 at 12:27 PM, Jos de Bruijn <jos.debruijn@gmail.com>wrote:

> As it seems [1] that equality and class membership formulas are not allowed
> to appear in facts, I propose to change the second bullet in section 2.3 of
> the RIF-Core spec [2] to:
>
> * Equality terms and class membership terms *cannot* occur in universal
> facts, variable-free atomic formulas outside of rule premises, or rule
> conclusions -- they are allowed only in rule premises.
>
>
> Best, Jos
>
> [1] http://lists.w3.org/Archives/Public/public-rif-wg/2010May/0054.html
>
>
> On Wed, May 12, 2010 at 11:10 AM, Jos de Bruijn <jos.debruijn@gmail.com>wrote:
>
>>
>>
>> On Wed, May 12, 2010 at 10:32 AM, Jos de Bruijn <jos.debruijn@gmail.com>wrote:
>>
>>> Axel, all,
>>>
>>> I think there are a number of basic problems in the specification of RIF
>>> Core formulas. In particular:
>>>
>>> 1- the notion of "rule conclusion" is never defined. In fact, neither the
>>> notion "rule" nor "conclusion" is defined anywhere. This leads to several
>>> ambiguities: e.g., is a variable-free rule implication a rule? perhaps. Is a
>>> variable-free atomic formula a rule? there is no wording in BLD that would
>>> suggest this.
>>>
>>> 2- if we were to assume that "rule" means "RIF-BLD rule", which is the
>>> assumption I would naturally make from the BLD spec, then I read the
>>> restriction
>>> "Equality terms and class membership terms *cannot* occur in rule
>>> conclusions -- they are allowed only in rule premises."
>>>
>>> in [1] as saying that equality terms and class membership terms are not
>>> allowing the the conclusions of RIF-BLD rules. Full-stop.
>>>
>>
>> s/allowing the/allowed in/
>>
>>
>>> This means they are allowed in variable-free rule implications, universal
>>> facts (although some text in BLD may suggest these are a kind of RIF-BLD
>>> rules), and variable-free atomic formulas.
>>> I am quite sure we decided not to allow the assertion of equality. I do
>>> not recall exactly what we decided about facts concerning class membership
>>> (i.e., a#b). Does anybody recall what we decided here?
>>>
>>> In any case, this ambiguity needs to be resolved. Notice that the EBNF
>>> grammar does not help us here, since it is non-normative.
>>>
>>>
>>> Best, Jos
>>>
>>> [1] http://www.w3.org/TR/2010/PR-rif-core-20100511/#Formulas_of_RIF-Core
>>>
>>> On Tue, May 11, 2010 at 6:15 PM, Axel Polleres <axel.polleres@deri.org>wrote:
>>>
>>>> Hi folks,
>>>>
>>>> We are working on a parser with some students and I am afraid my student
>>>> found something awkward in the RIF Core grammar, see mail below.
>>>>
>>>> Indeed, I think he poked into a quite weird issue:
>>>> It doesn't make sense to allow class membership terms in rule bodies, if
>>>> they can't appear at all in *any* facts.
>>>> The current grammar and the restrictions in Section 2.3 though only
>>>> allows uniterms and frames as facts.
>>>>
>>>>
>>>> To repair this
>>>>
>>>> 1) We'd need to change in Section 2.3 Formulas of RIF-Core:
>>>>
>>>>  * Equality terms and class membership terms cannot occur in rule
>>>> conclusions -- they are allowed only in rule premises.
>>>> -->
>>>>  * Equality terms cannot occur in rule conclusions -- they are allowed
>>>> only in rule premises.
>>>>  * Class membership terms can only occur in rule premises or as ground
>>>> facts.
>>>>
>>>> 2) a proposal to fix the grammar in Section 2.6 would  be:
>>>>
>>>> In the Rule Language grammar:
>>>>
>>>>  CLAUSE         ::= Implies | ATOMIC
>>>>  -->
>>>>  CLAUSE         ::= Implies | ATOMIC | GROUNDTERM '#' GROUNDTERM
>>>>
>>>>
>>>>
>>>> sorry for spotting this now only, but I am afraid this is severe.
>>>> the fix is not very problematic, though.
>>>>
>>>> Axel
>>>>
>>>>
>>>>
>>>>
>>>> Begin forwarded message:
>>>>
>>>> > From: "Obermeier, Philipp" <philipp.obermeier@deri.org>
>>>> > Date: 11 May 2010 16:26:50 GMT+01:00
>>>> > To: "Polleres, Axel" <axel.polleres@deri.org>
>>>> > Cc: "Marco Marano" <marcomarano83@gmail.com>
>>>> > Subject: RIF-Core: EBNF, equality/memberhip facts
>>>> >
>>>> > Hi Axel,
>>>> >
>>>> > I found a minor error in the EBNF grammar [1] for RIF-Core (Altough,
>>>> > this grammar is informative due to the lack of well-formedness checks,
>>>> > it is also defined as strict superset of RIF-Core.).  Within this
>>>> > grammar you cannot derive Equality or Membership (ground) facts since
>>>> > the ATOMIC rule's rhs is restricted to atomic formulas excluding
>>>> > Equality/Membership formulas. Apparently, this restriction is well
>>>> > justified since ATOMIC may appear in rule heads (cf. IMPLIES rule's
>>>> > rhs), for which Core forbids Equality and Membership formulas. In
>>>> > conclusion, an introduction of a new ATOMIC_FACTS grammar rule
>>>> extending
>>>> > ATOMIC by Membership/Equality  would solve this issue w/o breaking the
>>>> > restriction for atoms in rule heads.
>>>> >
>>>> > Best
>>>> > Philipp
>>>> >
>>>> > [1]
>>>> >
>>>> http://www.w3.org/2005/rules/wiki/Core#EBNF_Grammar_for_the_Presentation_Syntax_of_RIF-Core
>>>> >
>>>> > --
>>>> > Philipp Obermeier
>>>> > Digital Enterprise Research Institute, National University of Ireland,
>>>> Galway
>>>> > email: philipp.obermeier@deri.org
>>>>
>>>>
>>>
>>>
>>> --
>>> Jos de Bruijn
>>>  Web:          http://www.debruijn.net/
>>>  LinkedIn:     http://at.linkedin.com/in/josdebruijn
>>>
>>
>>
>>
>> --
>> Jos de Bruijn
>>  Web:          http://www.debruijn.net/
>>  LinkedIn:     http://at.linkedin.com/in/josdebruijn
>>
>
>
>
> --
> Jos de Bruijn
>  Web:          http://www.debruijn.net/
>  LinkedIn:     http://at.linkedin.com/in/josdebruijn
>



-- 
Jos de Bruijn
 Web:          http://www.debruijn.net/
 LinkedIn:     http://at.linkedin.com/in/josdebruijn
Received on Wednesday, 12 May 2010 10:33:29 GMT

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