shapes-ISSUE-33: Language Tags [Shacl-Req]

Requirement 4.6.4 must be clarified or separated in two requirements.

Requirement 6.4 reads as:

"R6.4: Expressivity: Language Tags

*Some constraints require comparing language tags of RDF literals, e.g. to
check that no language is used more than once per property. Also to produce
multi-lingual error messages.*"
When I voted in favour of it, I understood that it was about having a
mechanism to handle language tags in SHACL.

In a recent email:
https://lists.w3.org/Archives/Public/public-data-shapes-wg/2015Mar/0498.html
Richard says that given that this requirements is in the section "Complex
constraints" then it should not be part of the Lite/Core.

Although from my point of view, there is no boundary defined yet between
Lite/Core, I think having a simple mechanism to constraint which is the
language tag of string literals should be part of SHACL.

If it is necessary to add it as a single requirement, I would suggest to
have a new requirement which could be:

5.12: Language Tags

SHACL must have a mechanism to constraint language tags of RDF literals

6.4. Complex constraints on Language Tags

Some constraints require comparing language tags of RDF literals, e.g. to
check that no language is used more than once per property.

I would remove the last phrase: "*Also to produce multi-lingual error
messages." *
because it is about language errors. In fact I had already asked to remove
it in the Wiki:
https://www.w3.org/2014/data-shapes/wiki/Requirements#Expressivity:_Language_Tags

but it seems it was not removed and now it remains in the document.

-- 
-- Jose Labra