W3C home > Mailing lists > Public > public-rdf-dawg-comments@w3.org > March 2011

Re: !=, NOT IN and type errors

From: Eric Prud'hommeaux <eric@w3.org>
Date: Tue, 29 Mar 2011 05:17:00 -0400
To: Jeen Broekstra <jeen.broekstra@gmail.com>
Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, public-rdf-dawg-comments@w3.org
Message-ID: <20110329091657.GA12940@w3.org>
* Jeen Broekstra <jeen.broekstra@gmail.com> [2011-03-29 10:13+1300]
> On 27/03/2011 11:57, Eric Prud'hommeaux wrote:
> >* Jeen Broekstra<jeen.broekstra@gmail.com>  [2011-03-27 10:59+1300]
> 
> [snip]
> 
> >>Now, we apply RDFterm-equal to our comparison. Both operands are
> >>literals. The definition says that two literals are RDF-term-equal
> >>if they are "equivalent literals" according to def 6.5.1 in RDF
> >>concepts. Since our operands have different lexical values as well
> >>as different datatypes, literal equality fails. The definition of
> >>RDFterm-equal then says: "[it] produces a type error when both
> >>operands are literal but are not the same RDF term". Since in our
> >>case both are literal but are not the same term, it results in a
> >>type error. So RDFterm-equal results in a type error, and since
> >>applying fn:not on a type error results in a type error,
> >>"foo"^^xsd:string != "4"^^xsd:integer evaluates to a type error.
> >>This is what I originally thought happened, and what I thought was
> >>undesirable.
> >
> >Ahh, this is what I believe to have been the design goal. The problem
> >is exemplified by
> >   "iiii"^^my:romanNumeral = "iv"^^my:romanNumeral
> 
> Yes, quite, and I agree that this really the only way to handle
> non-native datatypes. It's the fact that it also works this way for
> native datatypes that annoys me. It leads to different SPARQL
> implementations giving different results for very basic comparisons.
> 
> >The answer there is probably a non-controversial "beats me". The
> >answer to "foo"^^xsd:string != "4"^^xsd:integer in unextended
> >implementations is also "beats me", but that doesn't keep you from
> >adding operators for e.g. xsd:string and xsd:integer for which the
> >answer to "=" is false. (You probably want a switch to enable you
> >to run the unextended tests, which have no way of distinnguishing
> >between sagely extension and wanton impudance.)
> 
> True. In fact I have already implemented this in Sesame this way
> (except for the switch bit). I am just of the opinion that it is
> unwise to leave this decision up to indivual implementations, at
> least for the native datatypes.
> 
> I would be much happier if the datatypes that SPARQL claims to
> support (that is, the ones mentioned in "Operand Data types") are
> indeed fully supported, i.e. it is fixed in the spec that string and
> int (and the other supported types) are pairwise distinct.
> 
> >We could take the bold step of declaring the 19 native types pairwise
> >distinct by either adding a bazillion rows to the operator mapping
> 
> Surely it doesn't need that many? The numeric types are already
> grouped under the nomer "numeric" (you could do the same for
> dateTime, date, etc, by the way, e.g. "calendar"). I'd say this
> would be enough:

Per parenthetical proposal for "calendar" group, interesting tactic,
but I think not yet necessary. SPARQL still appears to support only
xsd:dateTime (apart from dayTimeDuration, which should never equal a
dateTime).

> Op	type(A)		type(B)		maps to
> -----------------------------------------------
> A != B	string 		numeric 	TRUE
> A != B 	string 		boolean		TRUE
> A != B 	string 		calendar	TRUE
> A != B	numeric 	calendar	TRUE
> A != B	numeric 	boolean 	TRUE
> A != B	calendar 	boolean 	TRUE
> 
> Somewhat clunky, perhaps, but still managable I'd say.

It is indeed; I hadn't bothered evaluating "bazillion". This could be
tedious to evolve as SPARQL adopts more of the 17 xsd datatypes.


> >or
> >expanding the definition of RDFterm-equal like so:
> >[[
> >   Returns TRUE if term1 and term2 are the same RDF term as defined in
> >   Resource Description Framework (RDF): Concepts and Abstract Syntax
> >   [CONCEPTS];
> >+ returns FALSE if the arguments are different types but both are
> >+ listed in ยง17.1 Operand Data Types;
> 
> This is not quite enough as it does not check that the operands are
> _valid_ typed literals. You'd still want "xyz"^^xsd:integer !=
> "foo"^^xsd:string to raise a type error, I think.

* Jeen Broekstra <jeen.broekstra@gmail.com> [2011-03-29 11:09+1300]
> On 29/03/2011 10:13, Jeen Broekstra wrote:
> 
> [snip]
> 
> >This is not quite enough as it does not check that the operands are
> >_valid_ typed literals. You'd still want "xyz"^^xsd:integer !=
> >"foo"^^xsd:string to raise a type error, I think.
> 
> Minor addendum: it took me five seconds after hitting 'send' (I really
> hate it when that happens) to realize that this of course _also_ holds
> for the operator mapping table. Simply mapping != to 'true' will not
> quite be enough, it still needs the proviso that both operands have a
> correct lexical-to-value mapping.


> You could add that condition too I guess, but it all gets a bit
> convoluted - perhaps adding some rows to the mapping table is easier
> here?
> 
> Cheers,
> 
> Jeen

-- 
-ericP
Received on Tuesday, 29 March 2011 09:17:36 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Tuesday, 29 March 2011 09:17:37 GMT