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Re: RDF/XML Syntax Question: Label on an RDF Object being a literal

From: Danny Ayers <danny.ayers@gmail.com>
Date: Tue, 2 Mar 2010 04:52:01 +0100
Message-ID: <1f2ed5cd1003011952h10cae40ar52ff271b29432d7c@mail.gmail.com>
To: Pat Hayes <phayes@ihmc.us>
Cc: Damian Steer <pldms@mac.com>, Svante Schubert <Svante.Schubert@sun.com>, Semantic Web <semantic-web@w3.org>
On 2 March 2010 00:10, Pat Hayes <phayes@ihmc.us> wrote:

>
> Danny, the RDF specs are not wrong (on this matter, at least.) Neither
> mathematically nor technically. But it is necessary to actually read them
> and understand them.
>

ok Pat, how do you explain nominatives and text in the same space.

I am *not* a logician,  but I can see rubbish.


> Literals are textual objects, part of the RDF *syntax*, lIke URIs and blank
> nodes. Also like those, they - the literals - *refer to* things (in RDF
> Webspeak, resources.) Exactly what they refer to depends on the literal, and
> if the literal is typed, it depends on the datatype. So for example, the
> literal
>
> "345"^^xsd:number
>
> refers to the number three hundred and forty five.
> When you write RDF, all the names in the triples are understood to be
> talking about the things they refer to. So, this triple:
>
> ex:PatHayes  ex:hasAgeInYears "65"^^xsd:number .
>

Pat, no no no - ok literals are a syntactical thing, but don't we know
better into identifiers, resource (but not a string)


>
> says that my age is 65. It does not say that my age is "65", or that my age
> is a literal. It says that my age is a literal *value*, ie the value of a
> literal. The RDFS class rdfs:LIteral is not the class of literals: it is the
> class of literal *values*. There is no class of RDFS literals (at least, not
> one defined in RDFS), just as there is no RDFS-defined class of blank nodes
> or of URI references.
>
> Now, plain literals with no type (and no language tag) are a special case,
> in that their literal value is the literal string itself, so that
>
> ex:PatHayes foaf:name "Patrick John Hayes" .
>
> says that my name is the value of the literal "Patrick John Hayes", which
> is this very string itself. So in this case you can sort of refer to the
> actual literal. But its only in this plain-plain case, and as soon as you
> add a language tag or type the literal, this identity of syntax and value no
> longer holds.
>
> So to answer the original question, there is no way in RDF(S) (or indeed
> OWL) to *refer to* a typed literal. The intended use of literals is that
> they are to be used to refer to literal values, rather than be objects in
> their own right. To treat them as objects, we would need to have an RDFS
> meta-language for talking about RDFS syntax.
>
> Pat Hayes
>
> On Feb 28, 2010, at 5:31 PM, Danny Ayers wrote:
>
> I am not a logician, but I believe there has been some hair-tugging over
> the treatment of literals & resources. Technically and mathematically, it's
> wrong as it it stands in the specs. Bit strange given that the people behind
> it were the best in the world, but there you go.
>
> Until a reformulation of the RDF model comes along, we have to play with it
> pragmatically - a literal is a string etc.
>
> Please don't be scared by the fact that there are errors, it's usable, this
> stuff can be applied to the wire.
>
> The Italians say piano piano to mean we just do a little, and get their
> eventually.  A better saying is "may you live in interesting times", major
> curse. But that is where we are.
>
> Love,
> Danny.
>
> On 28 February 2010 23:34, Damian Steer <pldms@mac.com> wrote:
>
>> Sorry, substitute rdfs:label for ex:readableLabel there.
>>
>> Damian
>>
>>
>
>
> --
> http://danny.ayers.name
>
>
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>
>
>
>


-- 
http://danny.ayers.name
Received on Tuesday, 2 March 2010 03:52:34 UTC

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