problems with RDF datatyping

In trying to make the OWL semantics correspond to the RDF semantics I came
up with the following problems in RDF datatyping:

1/ A datatype is an element of IR, because the RDF MT says that datatypes are
denoted by URI references.  However, rdf:XMLLiteral is said to be a
datatype, but rdf:XMLLiteral is a URI reference.  Something is wrong here.

2/ XSD-interpretations include in their datatypes the XML Schema datatypes
that are problematic when removed from XML documents or have other
problems.  XSD-interpretations also include, for example, the datatype
named FOO, which is not defined as an XML datatype.

3/ A datatype has to be more than is specified in the RDF MT.  Except for
XSD-interpretations, which explicitly mention the URI-reference to datatype
relationship, there is no way of tying the intended URI-reference for a
datatype to that datatype.  For example, if I have D containing a datatype
for integers and a datatype for strings, there is no way to require that a
particular URI reference, say ex:int, denotes the integer datatype.


It probably makes more sense to say that a datatype is a four-tuple,
consisting of a URI reference, a lexical space, a value space, and a
lexical-to-value mapping.  


Peter F. Patel-Schneider
Bell Labs Research
Lucent Technologies