W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > January 2002

Re: Problem with TDL (NOT)

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Fri, 18 Jan 2002 08:49:39 +0200
To: ext Sergey Melnik <melnik@db.stanford.edu>, RDF Core <w3c-rdfcore-wg@w3.org>
Message-ID: <B86D9223.BCC6%patrick.stickler@nokia.com>
On 2002-01-18 4:42, "ext Sergey Melnik" <melnik@db.stanford.edu> wrote:

> Patrick,
> 
> there is a well-known problem with the rdf:type/rdf:value representation
> that you described in
> 
> http://www-nrc.nokia.com/sw/TDL.html
> 
> In essence, the interpretations of nodes _1 and _2 in
> 
> _1 rdf:value "3.0"
> _1 rdf:type us-double
> _2 rdf:value "3,0"
> _2 rdf:type german-double
> 
> fall together (_1 and _2 represent the same real value), and the pairing
> between the lexical representation and the type gets corrupted.
> Specifically, the semantics of the above four statements is equivalent
> to that of
> 
> _3 rdf:value "3.0"
> _3 rdf:value "3,0"
> _3 rdf:type us-double
> _3 rdf:type german-double
> 
> How do you suggest to work around this problem?

There is no problem.

The nodes _1 and _2 would *never* be merged in that fashion.

1. They do not denote the same value space member of the same
datatype as us-double is not the same datatype as german-double.

2. Neither anonymous nodes nor literal labeled nodes participate
in graph tidying.

The fact that the TDLs ("3.0",us-double) and ("3,0",german-double)
may correlate to the equivalent member in each other's value spaces or
in the value space of e.g. xsd:double is a matter
of interpretation -- not of representation.

E.g.

<rdfl:LexicalDatatype rdf:about="xsd:double"/>

<rdfl:LexicalDatatype rdf:about="us:double">
   <rdfl:lexicalSubClassOf rdf:resource="xsd:double"/>
</rdfl:LexicalDatatype>
 
<rdfl:LexicalDatatype rdf:about="german:double">
   <rdfs:subClassOf rdf:resource="xsd:double"/>
</rdfl:LexicalDatatype>

which defines, as we would expect, that the value
space of both us:double and german:double are subsets
of the value space of xsd:double but only the lexical
space of us:double is a subset of the lexical space
of xsd:double.

(note the difference between rdfs:subClassOf and
rdfl:lexicalSubClassOf!)

And if we know that the value spaces of us:double
and german:double are in fact a perfect intersection,
then we can also say

<rdfl:LexicalDatatype rdf:about="us:double">
   <rdfs:subClassOf rdf:resource="german:double"/>
</rdfl:LexicalDatatype>
 
<rdfl:LexicalDatatype rdf:about="german:double">
   <rdfs:subClassOf rdf:resource="us:double"/>
</rdfl:LexicalDatatype>

which says that any member of the value space of
us:double is also a member of the value space of
german:double and visa versa.

Thus, there is no problem.

The nodes in your example would never be merged, and
the relationships between the lexical and value spaces
of the datatypes in question are explicitly defined,
and interpretation about whether the two TDLs
("3.0",us-double) and ("3,0",german-double) denote
the same value happen outside the RDF-space, yet
the RDF representation -- using the TDL scheme -- is
fully sufficient for making that interpretation.

Cheers,

Patrick
 
--
               
Patrick Stickler              Phone: +358 50 483 9453
Senior Research Scientist     Fax:   +358 7180 35409
Nokia Research Center         Email: patrick.stickler@nokia.com
Received on Friday, 18 January 2002 01:48:47 EST

This archive was generated by hypermail pre-2.1.9 : Wednesday, 3 September 2003 09:43:55 EDT