W3C home > Mailing lists > Public > semantic-web@w3.org > August 2007

Re: what is a plain literal?

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Fri, 10 Aug 2007 11:11:52 +0100
Message-Id: <4E03962F-DB54-4B72-BABC-2F1FFC88377C@cs.man.ac.uk>
Cc: Semantic Web <semantic-web@w3.org>
To: Garret Wilson <garret@globalmentor.com>

On Aug 10, 2007, at 2:09 AM, Garret Wilson wrote:

>
> Everyone,
>
> I promise I'm not trying to dig up the "replace literals with  
> normal resources" discussion, although I'm still strongly for that  
> proposal. I have an honest question about plain literal semantics,  
> however. At http://www.w3.org/TR/2004/REC-rdf-mt-20040210/ 
> #urisandlit I read:
>
> "Plain literals are considered to denote themselves, so have a  
> fixed meaning."
>
> Is this a typo?

No.

> It's not the most natural sentence

I have no problem with the part you have problem with. (I'm not a fan  
of the "are considered to"  part rather than just "Plain literals  
denote themselves...".

> ---does it mean, "and thus always have a fixed meaning", or "and  
> and so have no fixed meaning?"

I have no idea why you are getting the second reading. Replace "so"  
with "thus". If you replace it with "thus not" you've clearly changed  
the meaning.

The semantic point is that plain literals always denote a particular  
object, whereas URIs (for example) can denote different things in  
different documents (or in different models of the same graph). That  
is, I can use http://example.org/soGreat to denote me and you can use  
it to denote you (each in our own Foaf file). In OWL, But I can only  
use "Bijan is so Great" to denote that very string. The meaning is,  
as they say, fixed.

> Next question: how do plain literals differ semantically from typed  
> literals with a datatype URI of xsd:string?

They can have a lang. Datatyped literals cannot. It was a big deal.  
It is clearly a wart.

[snip]

If I may make what is is intended to be a friendly comment: You are  
expending a ton of effort on the clearly marginal. That has  
significant opportunity costs.
Received on Friday, 10 August 2007 10:12:01 GMT

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