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Entailment Changes

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This is an informal, potentially incomplete summary of changes in entailment between RDF and RDF 1.1.

Most of the changes between RDF and RDF 1.1 do not have any effect on entailment, but there are a few minor changes.

The sequence in which the versions of entailment are defined has changed. Datatype entailment is now defined on top of simple entailment, and then RDF and RDFS entailment are defined. Datatype entailment formally refers to a set of 'recognized' datatypes, replacing the old datatype maps, but this does not have any effect on implementation.

RDF entailment has two required datatypes xsd:string and rdf:langString which must be recognized, but this doesn't appreciably add to RDF entailment as these two datatypes replace plain literals.

Literals formerly described as plain literals are now divided into xsd:string literals, for plain literals without language tags, and rdf:langString literals, for plain literals with language tags. Thus all literals have a type and there is no need for an implementation to have separate data structures for plain literals and datatyped literals, although rdf:langString is a special datatype as it has a language tag in addition to a lexical form and thus it requires special treatment. Implementations that have a special internal data structure for plain literals might not need to appreciably change. The zero Unicode character is not a valid element in xsd:string values, but was allowed in plain literals, so there is a minor change here.

One change that does affect entailment is that graphs containing invalid literals (e.g., "a"^^xsd:integer) are immediately inconsistent for recognized datatypes, even in sub-RDFS entailment regimes.

There is a list of XML Schema datatypes that are deemed suitable for use within RDF. They are all optional except for xsd:string.

The rdf:XMLLiteral datatype is now optional. rdf:HTML is a new optional datatype; implementation experience and illustrative tests are requested. (Note also that rdf:HTML has at-risk aspects concerning DOM4 normalization.) rdf:PlainLiteral is a newish optional datatype; implementation experience and illustrative tests are requested.

RDF 1.1 includes RDF Datasets. However, the semantics of RDF Datasets in RDF 1.1 is minimal and entailment per se is only defined on RDF graphs.