W3C home > Mailing lists > Public > public-webont-comments@w3.org > July 2003

[moved] RE: unsupported datatypes

From: Jim Hendler <hendler@cs.umd.edu>
Date: Wed, 16 Jul 2003 09:41:44 -0400
Message-Id: <p05200f0ebb3b0666b6ad@[]>
To: "Gary Ng" <Gary.Ng@networkinference.com>, "Ian Horrocks" <horrocks@cs.man.ac.uk>
Cc: <public-webont-comments@w3.org>

  Ian has suggested that he is happy to continue this discussion on 
www-rdf-logic, is that okay?
  Jim Hendler

At 6:26 PM +0100 7/15/03, Gary Ng wrote:
>>  -----Original Message-----
>>  From: Ian Horrocks
>>  Sent: 15 July 2003 18:02
>>  To: Gary Ng
>>  Cc: public-webont-comments@w3.org
>>  Subject: Re: unsupported datatypes
>>  On July 15, Gary Ng writes:
>>  >
>>  >
>>  > Another question, this time about unsupported datatypes.
>>  >
>>  > In the reference doc, it says:
>>  >
>>  > "For unsupported datatypes, lexically identical literals should be
>>  > considered equal, whereas lexically different literals would not be
>>  > known to be either equal or unequal. Unrecognized datatypes should
>>  > treated in the same way as unsupported datatypes."
>>  >
>>  > The first half of the sentence would suggest to treat a literal of
>>  > unknown type as just a string. However, I am not entirely sure what
>>  > expected from a reasoner with respect to the behaviour of "would not
>>  > known to be either equal or unequal".
>>  Unknown or unrecognised datatypes are treated as being the lexical
>>  form (a string) of some unknown datatype. It is obviously the case
>>  that, whatever the datatype, identical lexical forms map to the same
>>  element of the value space, and can thus be considered equal. For
>>  non-identical lexical forms, however, it *cannot* be assumed that they
>>  do not map to the same element of the value space and are thus
>>  unequal.
>>  E.g., the lexical forms "1.0" and "01.00" would map to the same value
>>  (and thus be considered equal) in some datatypes (e.g., decimal), but
>>  not in others (e.g., string).
>Yes, I got that.
>But from a practical point of view of handling values from an
>unsupported datatype within a reasoning tool, this sounds like I can't
>even implement them as strings because since two different strings would
>be considered unequal. So the question is, how should I implement them?
>Consider the following:
><Measurement rdf:ID="a_measurement">
>	<hasAValueOf
><Measurement rdf:ID="b_measurement">
>	<hasAValueOf
>by the definition, "XYZ" and "ABC" are neither equal nor unequal.
>So what should be the answer to the following question?
>Retrieve all instances of (complementOf(exists hasAValueOf XYZ))
>Because we cannot *prove* that XYZ = or != to ABC, thus
>The answer would be empty. Am I correct?
>If I am correct, then this behaviour is the same as if XYZ and ABC are
>classes/instances. So really we can't implement values from unsupported
>datatypes as strings.

Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  *** 240-277-3388 (Cell)
http://www.cs.umd.edu/users/hendler      *** NOTE CHANGED CELL NUMBER ***
Received on Wednesday, 16 July 2003 09:42:15 UTC

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