W3C home > Mailing lists > Public > www-webont-wg@w3.org > November 2002

decisions about RDF semantics

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 6 Nov 2002 23:01:48 -0600
Message-Id: <p05111b02b9efa06402a9@[65.217.30.130]>
To: www-webont-wg@w3.org
Cc: pfps@research.bell-labs.com

The RDF core WG is rapidly converging to a final version of RDFS, and 
this is a heads-up of some of the things that are relevant to the 
webont semantics.

SubClassOf and subPropertyOf now have IFF semantics, but range and 
domain don't. The community seems to be about evenly divided on this 
one, so if anyone has a strong case to make, then please make it 
quickly.

The RDF list vocabulary has essentially no semantics, so OWL will 
have to provide one. (The only assumptions are that
rdf:nil rdf:type rdf:List
and the obvious domain and range conditions on rdf:first and rdf:rest.)

There is very little datatyping provided. Literals can have datatypes 
attached, and when they do and when their string is a valid lexical 
form, they denote the appropriate value. Otherwise they are treated 
like opaque names, so OWL could impose its own interpretation on them 
in the absence of datatyping info. Bare literals always denote 
themselves (they can be a string or a pair of strings) and this is 
not influenced by datatyping. Datatype names used as class names 
refer to the class of elements of the value space of the datatype. 
There is no range datatyping and no provision for linking a bnode to 
a literal with a datatyping property, but such usage would not 
violate RDF, if OWL wanted to impose it. RDF *never* assumes that two 
items in different value spaces are equal, even when they are. If a 
datatype scheme wishes to make claims like this, it has to do so 
explicitly. RDF now has a single built-in datatype, rdfs:XMLLiteral, 
whose function is to be the 'XML-literal' marker. XML literals are 
the only typed literals that can be given a lang tag. There is a 
class rdfs:Datatype, whose members are datatypes (and datatype 
classes).

In case anyone wants to know, reified triples are understood to refer 
to triple tokens in a document, rather than to abstract grammatical 
forms.

OK, s'all for now.

Pat



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Received on Thursday, 7 November 2002 00:01:32 GMT

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