Re: adding {}s to grammar to address I18N-ISSUE-189

On Oct 7, 2012 10:35 AM, "Gavin Carothers" <gavin@carothers.name> wrote:
>
> On Sun, Oct 7, 2012 at 5:32 AM, Eric Prud'hommeaux <eric@w3.org> wrote:
> > The LC grammar includes a LANGTAG production
> >
> >   [144s] LANGTAG ::= '@' [a-zA-Z]+ ('-' [a-zA-Z0-9]+)*
> >
> > which doesn't match the one in BCP 47
> >
> >          obs-language-tag = primary-subtag *( "-" subtag )
> >          primary-subtag   = 1*8ALPHA
> >          subtag           = 1*8(ALPHA / DIGIT)
> >
> > (Basically, Turtle is too liberal in what it permits in a LANGTAG.)
> > The proposal from I18N was to reference
> >   http://tools.ietf.org/html/bcp47#section-2.1
> > which could mean one of:
> >
> > 1 remove the production rule and include instead (coursly) href the
bcp47 defn.
> > 2 preserve our production and href the bcp47 rule informatively
> > 3 preserve our production and href the bcp47 rule normatively
> > 4 align our production and href the bcp47 rule normatively
> >
> > I've mocked up #4 in the editor's draft (my pref). See the last
> > sentence of
> >
http://www.w3.org/2011/rdf-wg/wiki/I18n-Comments#189:_.5BS.5D_reference_obs-language-tag_instead_of_defining_your_own
> > for all the links.
>
> None of 1-4 provides an enhancement to the state of language tag
> parsing in Turtle. In order to use the grammar to test for a valid
> language tag it must be compared to the complete registration list,
> and be a legal composition. For even the lower bar of testing for a
> well formed language tag a much more complex grammar must be used. All
> of these solutions would simply add complexity without any real gain
> to anyone. RDF Concepts already requires, with a MUST no less,
> that "The language tag must be well-formed according to section
> 2.2.9", these additions to Turtle aren't enough to do that. Either we
> need to go all the way and specify the exhaustive grammar for well
> formedness or leave this alone and let something up stream of the
> parser confirm well formedness.

Tightening up the grammer for language tags provides exactly the
enhancement that the I18N group recommends. I am sympathetic to their
proposal, noting that it parallels our treatment of IRIs. We don't delve
into scheme specific validation, but our production is still intend to
eliminate crap up front.

> --Gavin
>
>
> > --
> > -ericP
> >