Re: Grammar presentation syntax FLD and BLD

>> Incidentally, I think there is a problem with the syntax for rules, as 
>> specified in FLD.  Namely, a rule is an implication phi :- psi; no 
>> quantification seems to be allowed. In the grammar below I also allowed 
>> rules with universal quantification.
> 
> There are also quantified formulas. In FLD you can have arbitrary quantifiers.
> I could have called phi :- psi a "Rule Implication" instead, but "Rule"
> seemed shorter and acceptable.

I guess this means an FLD rule set is a set of formulas?

>> I suppose that in the textual description which say that LITERAL and 
>> VARNAME are sequences of Unicode characters.
>> Actually, I would propose to make VARNAME just a sequence of 
>> alphanumeric characters
> 
> Why limit? Suppose some language allows non-alphanums in variables?

fair enough.

> 
>> and to always delimit LITERAL with double quotes.
> 
> Yes, I agree.
> 
>> Then, it is not really clear from [2] what the syntax is of the names in 
>> named-argument predicates and functions.  I would propose these names to 
>> be absolute IRIs.
> 
> Are you talking about the names of the arguments or the names of the
> predicates? For the former, Const is not right. They are ArgNames, where an
> ArgName is a seq of unicode chars (again, why limit to alphanums?).
> There is a mistake in the BNF (in the current version of the FLD/BLD document).
> For the latter,  the pred names are Const'ants. As a special case, they can
> be IRIs.

I was talking about the names of arguments.  To me it would make most 
sense that these are IRIs, but I'm fine with them being sequences of 
Unicode characters.


>> Another thing: why do we allow nesting of Forall statements in rules if 
>> one can already specify multiple variables?
>> I would propose to either remove the nesting or only allow mentioning of 
>> 1 variable. I would prefer the former.
> 
> This is also a mistake in the current version of BNF in the document. Note
> that the formal syntax does not allow that. (Of course, BNF defines a
> superset of the language, so it is strictly speaking not a mistake :-)
> 
> Note that the formal syntax uses "universal" for what BNF calls a "rule".
> These universals correspond to "Implies" in BNF. Unfortunately, Implies is
> not so good, if FLD is taken into the account, since FLD can have two kinds
> of "implies": :- and <-. Currently, <- is not used in FLD, but it could be,
> so it is better to avoid the confusion.

Actually, I was proposing to get rid of "Implies" in BNF, because I was 
not convinced of its usefulness.

Could you actually point me out where the implication <- is defined in 
FLD?  I could not find it.

Best, Jos

> 
> Proposals for better names would be appreciated.
> 
> 
> 	--michael  

-- 
                          debruijn@inf.unibz.it

Jos de Bruijn,        http://www.debruijn.net/
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