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From: <parcher@icra.org>
Date: Tue, 20 Nov 2007 16:59:16 -0000 (GMT)
Message-ID: <16311.>
To: public-powderwg@w3.org

More comments inline.

> On Mon Nov 19 17:50:01 2007 Phil Archer said:
>> It seems to me we need to find the best compromise between two extremes:
>> 1. Just publish the data in a simple format and tell people how to
>> process
>> it if they want to. Whilst this would be machine-readable, it is not
>> really
>> machine-processable in an automated, generalised environment.
>> 2. DRs become a set of (potentially very complex) rules, something like:
>> IF ICRAdescriptionResource( ?d ) AND
>> temporal:hasValidTime(?d, ?period) AND
> [snipped]
> One possible compromise, to be considered by the group, is the
> following: let DRs and groups be RDF resources, without trying to cast
> them into OWL or any other formal semantics.

That's more or less where we were heading until the Boston meeting. The
problem is that it means you end up publishing data that looks like RDF
but that actually isn't so it's inevitable that some Sem Web tools will
get the wrong answer by doing the right thing so to speak.

> The implementor is free to
> choose whatever mechanism it best suited for treating the data (which
> almost centrainly isn't going to be OWL or SWRL reasoning). The
> implementor is responsible for guaranteeing that descriptors get copied
> from DRs to the actual resources being described, whenever the DR is
> applicable (is still valid and the resourse is withing the DR's scope).


> which says that ChildSafeStrict resources are:
> (a) ChildSafe themselves, AND
> (b) only link to ChildSafe resources.
> The need for such a rule would justify resorting to as expressive a
> language as OWL, but would also mean that no simpler "front-end" can be
> used, as anything expressive enough will also have to be complex enough.

We've been careful to keep everything as general as possible, especially
where the trust element is concerned. Section 6 of the current public
draft of the DR doc [1] offers a range of possible methods by which trust
can be placed in a DR. As the preamble says, the level of trust you need
in a Web site about children's parties is different from the level of
trust you need in nuclear installation safety, so the group has agreed
that no one method should be taken as 'the trust model' to be used.

We are looking at OWL only because it appears to do what we need - which
is to provide a method through which we can publish a definition of, say,
'mobileOK' and a resource set and find out that the resource set is
mobileOK. Importantly, it allows us to publish data in a format that won't
be misunderstood by existing tools.

We do not 'want to use reasoners' - if reasoners can't do what we want
then we'll use/invent something that can. There are, of course, very good
reasons for the limits of expressivity of DL - which is fine if what you
want to do is reasoning. We don't: we want to know what is mobileOK, what
is accessibile, what is trustworthy etc.


> If you can precisely specify what it is that needs to be done with the
> information in foaf:maker, it will help a lot. For example, will it be
> used to simply let browsers black-list or white-list labelling
> authorities? Or will it be involved in the classification, e.g.:

We use foaf:maker to point to the entitly that created the DR. We use
foaf:maker rather than dc:creator because the semantics are better -
dc:creator points to a string; foaf:maker points to an instance of the RDF
Class foaf:Agent which has teh useful subclasses foaf:Person and

The foaf:Agent class is where you find the information you can use to
determine whether or not you trust a given DR and, usually, you'll also
find information on how to authenticate the data. So the ICRA foaf file
will say something like:

<foaf:Organization rdf:ID="me">
  <foaf:homepage rdf:resource="http://www.fosi.org/" />
  <foaf:fundedBy>Membership drawn largely Internet Indusrty, plus
rdf:resource="http://checked.icra.org/authentication" />

The foaf:maker attribute is critical! Without it, POWDER isn't POWDER.

> IF 3 or more authories say it is ChildSafe
> THEN it is ReallyChildSafe

That's a rule that an implementor might define and use but it's beyond the
scope of POWDER. What we're about it providing the data that can be used
in rules, whether written in a semantically-rich environment or just a
straightforward Boolean statement.


[1] http://www.w3.org/TR/2007/WD-powder-dr-20070925/#trust
Received on Tuesday, 20 November 2007 16:59:39 UTC

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