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

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 1 Mar 2010 23:08:40 -0600
Cc: Damian Steer <pldms@mac.com>, Svante Schubert <Svante.Schubert@sun.com>, Semantic Web <semantic-web@w3.org>
Message-Id: <D233632D-51A5-488F-A82C-B2DF9F98A8DC@ihmc.us>
To: Danny Ayers <danny.ayers@gmail.com>

On Mar 1, 2010, at 9:57 PM, Danny Ayers wrote:

> Burp, sorry Pat, gotta try again.
>
> Literal strings and http resources are poles apart, surely?
>
> One is identified by the name it has been given (hopefully http  
> something) and the other you can twist about, make a hash of or  
> whatever - but it's still a string.
>

First, what exactly do you mean by "http resource"?  The W3C has, in  
its wisdom, chosen to use the word "resource" to mean, anything.  
Anything, really. A web page about Moby Dick is a resource, but so is  
the book Moby Dick itself, and so is my old tatty copy of it, and so  
is its dead author. Everything is a resource, and RDF is supposed to  
be able to talk about all of them. There isn't anything in the W3C  
specs that refers to 'http resource', as far as I know. Im going to  
guess that you mean things like web pages, things that have  
representations that can be sent in response to an HTTP GET request.  
So yes, strings and "http resources" are different kinds of thing,  
indeed. So what is your point, exactly? Who said they weren't  
different kinds of thing? And what has this to do with RDF? Web pages,  
novels about whales, physical books on a shelf and dead authors are  
also different kinds of thing, but they are all resources, all  
describable by RDF.

I guess (?) that your point is that since literals are based on  
strings (simple plain literals *are* strings) and URIs identify http  
resources, they must be as different as chalk from cheese. Is that  
more or less right? Because there are two things wrong with this, um,  
argument. First, you are comparing literals themselves with the things  
that URIs refer to. But if you were to compare literals with URIs,  
they are in fact both strings of characters. They both have syntax  
rules and need to be parsed. They are both kinds of name, in fact. And  
if you were to compare literal values, which literals refer to, with  
the resources that URIs refer to, then again you will see a  
similarity, in that (as far as RDF is concerned) these can both be  
anything. Datatype values even for XSD datatypes include numbers,  
dates and XML documents. There are proposals for datatypes with values  
including RDF graphs and colors. Pretty much any collection of things  
that has a widely recognized 'standard' naming system could be used as  
literal values. For example, we could have a datatype for books, in  
which the ISBN number is the literal string and the actual book is the  
literal value. The point being that it is not at all broken to have a  
URI and a literal identifying the same thing, and that there are a lot  
more kinds of thing than just "http resources".

By the way, strings are things too, and they also can be identified by  
URIs. For example,

http://dbpedia.org/resource/Gettysburg_address

identifies the string

"Four score and seven years ago our fathers brought forth on this  
continent, a new nation, conceived in Liberty, and dedicated to the  
proposition that all men are created equal. Now we are engaged in a  
great civil war, testing whether that nation, or any nation so  
conceived and so dedicated, can long endure. We are met on a great  
battlefield of that war. We have come to dedicate a portion of that  
field, as a final resting place for those who here gave their lives  
that that nation might live. It is altogether fitting and proper that  
we should do this. But, in a larger sense, we cannot dedicate—we  
cannot consecrate—we cannot hallow—this ground. The brave men, living  
and dead, who struggled here, have consecrated it, far above our poor  
power to add or detract. The world will little note, nor long remember  
what we say here, but it can never forget what they did here. It is  
for us the living, rather, to be dedicated here to the unfinished work  
which they who fought here have thus far so nobly advanced. It is  
rather for us to be here dedicated to the great task remaining before  
us—that from these honored dead we take increased devotion to that  
cause for which they gave the last full measure of devotion—that we  
here highly resolve that these dead shall not have died in vain—that  
this nation, under God, shall have a new birth of freedom— and that  
government of the people, by the people, for the people, shall not  
perish from the earth."

Make sense?

Pat


Received on Tuesday, 2 March 2010 05:09:48 UTC

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