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POWDER: resource descriptions as a semantic extension

From: Jeremy Carroll <jjc@hpl.hp.com>
Date: Fri, 14 Dec 2007 22:06:41 +0000
Message-ID: <4762FE71.5000906@hpl.hp.com>
To: www-archive@w3.org, Phil Archer <parcher@icra.org>, "Carroll, Jeremy John" <jeremy.carroll@hp.com>, Dan Brickley <danbri@danbri.org>, "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>
CC: Ivan Herman <ivan@w3.org>, Bijan Parsia <bparsia@cs.man.ac.uk>

Jeremy Carroll wrote:

> - resource descriptions, as a semantic extension??
>   RDF semantics makes no provision for examining the IRIs used for 
> resources. This is not addressed by OWL 1.0 or OWL 1.1. This is 
> fundamental to POWDER; and should, in my view, be addressed by formally 
> creating a suitable semantic extension.


I wonder a bit whether a ResourceSet

http://www.w3.org/TR/2007/WD-powder-grouping-20071031/

should be a class of web resources or a class of URIs.
For now, I'll follow the class of web resources view that is in the 
design in the WD.

If we consider a property such as wdr:includeHosts, it is intended to 
constrain the resource set in a particular way.

There are two aspects to this constraint:
- it refers to the resource identified by URIs using that host
- it is intended to talk about the representations which are accessed 
when you GET the resource

RDF does not explicitly relate to the operations of GET ... rather the 
relationship between Resource and Representation is left to RFC 3986.

Moreover, RDF semantics, does not really tslk about the resource 
identified by a URI - rather it talks about model theoretic 
interpretations I

RDF MT: [[
The semantics does not assume any particular relationship between the 
denotation of a URI reference and a document or Web resource which can 
be retrieved by using that URI reference in an HTTP transfer protocol, 
or any entity which is considered to be the source of such documents.
]]

We want to specify additional semantic conditions on the wdr vocab such 
as wdr:includeHosts

Also in RDF MT we read:[[
Particular uses of RDF, [...], may impose further semantic conditions in 
addition to those described here, and such extra semantic conditions can 
also be imposed on the meanings of terms in particular RDF vocabularies. 
Extensions or dialects of RDF which are obtained by imposing such extra 
semantic conditions may be referred to as semantic extensions of RDF. 
Semantic extensions of RDF are constrained in this recommendation using 
the keywords MUST , MUST NOT, SHOULD and MAY of [RFC 2119]. Semantic 
extensions of RDF MUST conform to the semantic conditions for simple 
interpretations described in sections 1.3  and 1.4 and 1.5 and those for 
RDF interpretations described in section 3.1 of this document.
]]

As an example, with the wdr:includeHosts property, I think we can 
formally define an extension including it, in which the formal meaning 
corresponds to the informal meaning in the WD, as follows:

<x,sss> is in IEXT(I(wdr:includeHosts)) iff
  x is in IC
  sss is a string, which when understood as a space-separated list of 
strings lll,
  and for every r in ICEXT(x)
     there is a URI uuu in the domain of I, with I(uuu)=r
     and lll has an element hhh, also a string, such that when uuu is 
normalized as specified in section 2.1.3, the host part of uuu ends with 
hhh.

For me, it would suffice to do that for one includeZZZ property and one 
excludeZZZ property, and then to say that for the others, the informal 
description, corresponds to a similar model theoretic description.

Thus, it should be possible to describe the whole semantic extension in 
a fairly small amount of text.

Jeremy



there is some URI u in the vocabulary of I, which, when normalized
Received on Friday, 14 December 2007 22:07:34 GMT

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