Recognize rdf:dirLangString

[afs]

This closes #59.
Replacement for PR #60.

This PR includes updates for the "Semantic conditions for literals table" and "RDFS semantic conditions".

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Preview | Diff

[gkellogg]

On tiny grammar change. Otherwise, looks good.

[pfps]

I believe that there needs to be a WG decision to add this. I created w3c/rdf-star-wg#139 for this purpose.

(The request changes flag is only to prevent yet another rogue merge.)

[afs]

I believe that there needs to be a WG decision to add this.

There has been this WG resolution

support initial text direction in RDF Language-Tagged Literals

and this WG resolution

Add base direction as a forth element of Literals

and this WG resolution

Accept RDF-Concepts issue "text direction"

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RDF 1.1 Semantics has it's own description of datatypes - it needs updating.

Why is rdf:langString required?

RDF 1.1 Semantics calls out rdf:langString as a normative "exception" because it has a special value mapping from RDF term to value. It gives a fixed (normative) mechanism for rdf:langString that includes handling the language tag in a case insensitive manner. Semantic extensions must agree on this exception.

RDF 1.2 Semantics must do so for rdf:dirLangString with a compatible mechanism, adding dealing with base direction. This PR uses the same text wording style to emphasis this.

The same is true for rdf:dirLangString in order to enact the WG resolutions, making it available for semantic extensions with the same interpretation for all semantic extensions.

Otherwise, the text of RDF Semantics need significant revision because it talks in general terms about the datatype mapping lexical space to value space.

[pfps]

Part of this PR is

RDF processors are not required to recognize any datatype IRIs other than
xsd:string,
rdf:langString, and
rdf:dirLangString
I don't believe that the requirement to recognize directional language strings has been decided.

[afs]

Why is rdf:langString required?

[gkellogg]

I believe the need to support rdf:dirLangString semantics is implicit in the other approvals. Indeed, if it were not a recognized datatype with conditions based on rdf:langString it would be inconsistent. The Working Group's time is quite limited, and easily gets taken up on perm-threads. No need to add further burden to go over something that is so clearly necessary. If there are reasonable objections, they can be made here, or in #60.