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>

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/josdebruijnReceived on Wednesday, 12 May 2010 10:33:29 GMT

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