- From: Jos de Bruijn <jos.debruijn@gmail.com>
- Date: Wed, 12 May 2010 12:27:51 +0200
- To: RIF <public-rif-wg@w3.org>
- Message-ID: <AANLkTimmsZxQIDKbRgcyuY_tFocAQOMCiIYrUorPew-b@mail.gmail.com>
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
Received on Wednesday, 12 May 2010 10:28:46 UTC