- From: Dave Beckett <dave.beckett@bristol.ac.uk>
- Date: Wed, 6 Apr 2005 10:34:50 +0100
- To: Patrick Stickler <patrick.stickler@nokia.com>
- Cc: "ext Pat Hayes" <phayes@ihmc.us>, www-rdf-comments@w3.org, Arjohn Kampman <arjohn.kampman@aduna.biz>
- Message-ID: <20050406103450.09ffcfb4@hoth.ilrt.bris.ac.uk>
(re-editing to remove top-quoting so time goes forward) > On Apr 5, 2005, at 20:02, ext Pat Hayes wrote: > > > > Im presuming that "" means the empty string, right? I don't think > > there are any serious issues if that is true. For example, > > ""^^xsd:string makes sense (I think. Its rather hard to discover if > > the XML schema spec allows empty strings) but ""^^xsd:number doesn't > > because the empty string isn't a legal lexical form for xsd:number. xsd:string ( http://www.w3.org/TR/xmlschema-2/#string ) does not define any lexical representation (!) but assuming it is the value space, [[the set of finite-length sequences of characters]] then "" is an allowed lexical form xsd:number I assume is a typo, there's no such type. xsd:integer ( http://www.w3.org/TR/xmlschema-2/#integer ) does not seem to forbid "" either, as a [[finite-length sequence of decimal digits]] can also be 0-length, although what value has lexical form "" is not defined. xsd:decimal ( http://www.w3.org/TR/xmlschema-2/#decimal ) is similar. The canonical represetnation requires a '.' so cannot be empty but that does not prevent the lexical form "". and so on > > There might be some issues if we needed to have 'empty values' in > > value domains, but I don't see that arising here. I think such datatype interpretation work is outside of RDF; as long as the lexical forms (always unicode strings) are encodable, it is ok. No reasons somebody could not have "NULL"^^my:sql or ""^^my:sql On Wed, 6 Apr 2005 09:48:14 +0300, Patrick Stickler <patrick.stickler@nokia.com> wrote: > OK. Thanks, Pat. So then for datatypes which do not > have null lexical forms we treat a null lexical form the 'null' isn't a good term to use here, it's a 0-length lexical form or unicode string. null would more be in terms of datatype values? > same as any other invalid lexical form. I.e. both > > ""^^xsd:number > "abc"^^xsd:number > > are both invalid, for the same reason, that the specified > lexical forms are not in fact in the lexical space of the > specified datatype. They are only datatype-invalid under some datatype interpretation (here XSD). They are still valid RDF Typed Literals: [[If the lexical form is not in the lexical space of the datatype associated with the datatype URI, then no literal value can be associated with the typed literal. Such a case, while in error, is not syntactically ill-formed.]] -- http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#section-Literal-Value i.e. it's not an illegal RDF triple but it is an "ill-typed literal", see "The third condition" of http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#DTYPEINTERP > We then leave it up to the "owners" of a given datatype > to clarify whether or not the null lexical form is or > is not a member of the lexical space of the datatype. Yes, which is outside RDF, per RDF Core's datatype design. http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#section-Datatypes-intro Dave
Received on Wednesday, 6 April 2005 09:36:57 UTC