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Re: Datatyping Summary

From: Martyn Horner <martyn.horner@profium.com>
Date: Wed, 30 Jan 2002 12:24:32 +0100
Message-ID: <3C57D7F0.33037DA3@profium.com>
To: Jeremy Carroll <jjc@hplb.hpl.hp.com>
CC: w3c-rdfcore-wg@w3.org
Jeremy Carroll wrote:
> 
...
> If we are talking about the values, then the query is only true if we have
> compatible type declarations for both literal nodes. Since we are not, we
> cannot conclude that
>   The age of mary is the title of the film.
> hence we avoid the error.
> 
> If on the other hand we are talking about the lexicalizations we have:
>    The age of mary as a string is the title of the film as a string.
>    i.e. 10 as a string is "10" as a string

Assuming that the lexicalization is canonical. Back to the `age of Mary
as a string' expressed as octal or as "010", again.

My problem from the query side is that it is a desirable application
function to define equivalence for each datatype in a liberal manner -
albeit only locally. Thus two literal dates may be equal according to
ISO8601 though their strings are not. Even strings in practice can be
usefully equated modulo whitespace trimming, etc.

If you try and do this sort of cross-type equation in practice then you
cannot use any locally sanctioned equality conventions (from which
side?) and you're reduced to pedantic char-by-char comparison.

This isn't a fundamental comment on RDF as such but belongs in the area
of:
> 
> So TDL assists the application developer in being logically correct.
> 
TDL probably also allows the application developer to be more helpful.

The lex-value mapping for a datatype may include non-trivial conversions
which make queries as the above very frustrating if not downright silly:
the birthdate of Mary as a string is the same as her encrypted password
expressed in decimal - pure nonsense.

> ----
> 
> Brian, I would be very much obliged if you can condense this example to add
> to your summary list of concrete "can't live with" issues on the proposals.
> My title would be "S-B encourages logically errors in the application type
> processing."
> 

-- 
Martyn Horner <martyn.horner@profium.com>
Profium, Les Espaces de Sophia,
Immeuble Delta, B.P. 037, F-06901 Sophia-Antipolis, France
Tel. +33 (0)4.93.95.31.44 Fax. +33 (0)4.93.95.52.58
Mob. +33 (0)6.21.01.54.56 Internet: http://www.profium.com
Received on Wednesday, 30 January 2002 06:25:21 EST

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