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RE: Subjects as Literals

From: Michael Schneider <schneid@fzi.de>
Date: Tue, 6 Jul 2010 23:40:10 +0200
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A001F07FED@judith.fzi.de>
To: <nathan@webr3.org>
Cc: "Linked Data community" <public-lod@w3.org>, "Semantic Web" <semantic-web@w3.org>
Nathan wrote:

>Sent: Tuesday, July 06, 2010 11:02 PM
>To: Pat Hayes
>Cc: Toby Inkster; Linked Data community; Semantic Web
>Subject: Re: Subjects as Literals
>
>Pat Hayes wrote:
>> However, before I lose any more of my SW friends, let me say at once
>> that I am NOT arguing for this change to RDF.
>
>so after hundreds of emails, I have to ask - what (the hell) defines
>RDF?
>
>I've read that 'The RDF Semantics as stated works fine with triples
>which have any kind of syntactic node in any position in any
>combination.'
>
>Do the 'RDF Semantics' define RDF? or do the serializations?

Every formal language is essentially defined by a (abstract) syntax and a
semantics. The syntax defines which well-formed syntactic constructs exist,
and the semantics gives meaning to these constructs. 

RDF is defined by the RDF Abstract Syntax, defined in [1], and the RDF
Semantics, defined in [2]. 

Serializations of the (abstract) syntax, as RDF/XML [3] or N3 in the case of
RDF, are concrete formalisms to encode the abstract syntax of a language
into a stream of characters so a language construct can be technically
stored and processed. A serialization does not fundamentally contribute to
the specification of the language, but is of great importance anyway. An
abstract syntax cannot really be stored or processed, but is more of a
conceptual/mathematical model.

>simply - does RDF support literal subjects or not - I've read the
>aforementioned sentence to read 'RDF Semantics support literal subjects'
>or should I be reading 'RDF Semantics could support literal subjects' or
>'does support literal subjects' or?

The RDF Semantics could, in principle, cope with generalized RDF, but the
RDF Abstract Syntax does not support literal subjects. Therefore, RDF as a
whole does not support literal subjects.

>Just seeking a definitive bit of clarity on 1: what defines RDF, 2: what
>is *currently* supported in that definition.
>
>Preferably a serialization unspecific answer :)

Indeed. Even if a serialization of RDF would support literals in subjects,
RDF as a formal language would still not support it. For instance, N3
supports certain forms of rules, and TriG supports named graphs. But none of
these syntactic constructs are supported by the RDF Abstract Syntax. So they
are not supported by RDF. 

>Best & TIA,
>
>Nathan

Best,
Michael

[1] <http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/>
[2] <http://www.w3.org/TR/2004/REC-rdf-mt-20040210/>
[3] <http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/>

--
Dipl.-Inform. Michael Schneider
Research Scientist, Information Process Engineering (IPE)
Tel  : +49-721-9654-726
Fax  : +49-721-9654-727
Email: michael.schneider@fzi.de
WWW  : http://www.fzi.de/michael.schneider
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Received on Tuesday, 6 July 2010 21:40:45 UTC

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