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[DTB/Abridged syntax] ISSUE on -equals and -not-equals predicates?

From: Axel Polleres <axel.polleres@deri.org>
Date: Thu, 04 Dec 2008 16:21:17 +0000
Message-ID: <4938037D.9030705@deri.org>
To: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>

Hi,

I introduced, as for the other datatypes (along with an editors note),
-equals and -not-equals predicates for the rdf:XMLLiteral datatype.

There is an obvious overlap between the -equals predicates and '=', i.e. 
the '=' built-ins are superfluous, it seems, for dialects that support 
equality.

That is not the case for the not-equals predicates, though:

All the -not-equals predicates, i.e.  pred:numeric-not-equal, 
pred:string-not-equal, pred:dateTime-not-equal, pred:date-not-equal, 
pred:time-not-equal, pred:duration-not-equal, pred:XMLLiteral-not-equal, 
pred:text-not-equal

are defined on the same domains as their positive counterpart with 
reversed truth-values.

That has the consequence though, that they are not possibly emulated by
negation as failure, i.e. it is in general not true to say that the

-not-equals version is true, whenever the -equals version is NOT true.


An example:

  _a:-  External (pred:numberic-equals("blabla", 1) )
  _b:-  External (pred:numberic-not-equals("blabla", 1) )

entails neither _a nor _b, however

  _a:-  "blabla" = 1
  _b:-  naf ( "blabla" = 1 )

would entail _b.

So, 2 questions:

1) Do we want this behavior or do we want the negation as failure 
behavior of inequality?
2) Do we want the redundancy of equals predicates?

I think we need these things clarified, to be able to determine how
'=' and "!=" shortcuts in an abridged syntax should be defined.

Axel



-- 
Dr. Axel Polleres
Digital Enterprise Research Institute, National University of Ireland, 
Galway
email: axel.polleres@deri.org  url: http://www.polleres.net/
Received on Thursday, 4 December 2008 16:22:05 GMT

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