From: Jos de Bruijn <jos.debruijn@gmail.com>

Date: Wed, 12 May 2010 11:10:43 +0200

Message-ID: <AANLkTinv-PBIEOLWJqTRSd4tNdBvN9W65WJ-nBxg-zJX@mail.gmail.com>

To: RIF <public-rif-wg@w3.org>

Date: Wed, 12 May 2010 11:10:43 +0200

Message-ID: <AANLkTinv-PBIEOLWJqTRSd4tNdBvN9W65WJ-nBxg-zJX@mail.gmail.com>

To: RIF <public-rif-wg@w3.org>

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/josdebruijnReceived on Wednesday, 12 May 2010 09:11:36 UTC

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