W3C home > Mailing lists > Public > public-powderwg@w3.org > November 2007

Re: New DRs

From: Andrea Perego <andrea.perego@uninsubria.it>
Date: Mon, 26 Nov 2007 12:02:37 +0100
Message-ID: <474AA7CD.7020204@uninsubria.it>
CC: Public POWDER <public-powderwg@w3.org>

> Thanks very much for this Andrea - it's a very helpful summary and, as I
> think you know, this is the method I believe we should use. It is simple
> to understand and, not unimportantly, simple to represent in pictures [1].

Thanks, Phil.

> I do however disagree very slightly with one of your conclusions on the
> (critical) issue of the reification statements - I believe it _is_ OK to
> put all the validity information in the same single block of data as the
> foaf:maker link and for the extra reification to be optional. Taking
> your basic attribution statement:
> <rdf:Description rdf:about="#claim1">
>   <foaf:maker rdf:resource="http://www.example.org/foaf.rdf#david" />
> </rdf:Description>
> This says that _claim1_ was made by David. Let's add in the validity stuff:
> <rdf:Description rdf:about="#claim1">
>   <foaf:maker rdf:resource="http://www.example.org/foaf.rdf#david" />
>   <dcterms:issued>2006-12-31</dcterms:issued>
>   <wdr:validFrom>2006-12-31</wdr:validFrom>
>   <wdr:validUntil>2006-12-31</wdr:validUntil>
> </rdf:Description>
> This says that claim 1 was made by David, issued on the given date and
> is valid between the dates given.
> As you say, this does _not_ make it unambiguous that it is David saying
> that the claim was issued on a certain date. Indeed, the person saying
> it was issued on a given date is not specified but if I know:
> - it was David that said it;
> - when it was said;
> - when it will stop being said;
> Is this more useful in the real world than knowing
> - it was David that said it;
> - when David says he said it;
> - when David says he will stop saying it;
> The two are different - the second is more complete - but does it make
> such a difference to the usability of the data that we should require
> the extra detail?
> My proposal would be that we specify that a DR MUST include first level
> reification to provide details about who made the claim that
> ResourceOnExampleDotOrg is a sub class of ResourceSafeForChildren and
> that this MUST be done using foaf:maker (as you say, this is the essence
> of a DR - it's what makes POWDER what it is and not just an RDF/OWL
> application). I would then say that a DR publisher MAY add additional
> data to describe the maker of any additional assertions about the claim,
> such as who says it was issued on a given date and will expire on
> another date.

I completely agree with your view. Actually, what I meant to do in my
previous mail was to highlight some critical points. So, it must be
clear that, if we specify this:

<rdf:Description rdf:about="#claim1">
  <foaf:maker rdf:resource="http://www.example.org/foaf.rdf#david" />

the actual meaning will be:
- (someone says that) statement #claim1 has been made by David
- (someone says that) statement #claim1 has been issued on 31 Dec 2006
- (someone says that) statement #claim1 is valid for the period 1 Jan
2007 - 31 Dec 2007

So, this *does not mean* that the issue date and validity period have
been specified by David.

> I believe it _is_ a very big flaw if we end up saying that a DR must
> exist as a discrete ontology - it makes the publication and querying of
> bulk data more complicated and it's the bulk data that is going to be
> most useful to applications.
> From our (shared) experience of working with RDF-CL, if a Web site wants
> to include an IQUA and an ICRA label, it makes sense to put them in the
> same file but we get into all sorts of bother with the isAuthorityFor
> property on the labels.rdf file itself because, well, they came from
> different authorities - and that's just two labels in one RDF instance.

I agree with you that we shouldn't state that a file can contain at most
1 DR. However, I would highlight that the problem we have with
reification is that, by specifying:

<rdf:Description rdf:about="#claim1">
  <foaf:maker rdf:resource="http://www.example.org/foaf.rdf#david" />

we are indicating just the author of the rdfs:subclassOf statement
concerning the OWL classes ResourceOnExampleDotOrg and
ResourceSafeForChildren, but not the author of those class definitions.
In order to obtain this we should include in the rdf:Description above a
statement for each of the statements used to define those classes.

By contrast, by using owl:Ontology or foaf:Document (or something
similar), we can specify with just one statement the author of the whole
content of the file. The problem, as it has already been said, is that,
by doing this, we can include just one DR in the same file.

Actually, to be precise, this is not exactly true. In fact, if the same
file contains, say, 3 DRs having the same author, validity period, issue
date, the set of statements:

<owl:Ontology rdf:about="">
  <foaf:maker rdf:resource="http://www.example.org/foaf.rdf#david" />

applies to all of them, and thus we don't need to use reification. By
contrast, if such DRs have in common just the author, we can specify:

<owl:Ontology rdf:about="">
  <foaf:maker rdf:resource="http://www.example.org/foaf.rdf#david" />

and use reification for validity period and issue date.

Probably the approaches based on reification and
owl:Ontology/foaf:Document can be considered as two possible solutions
which can be combined, if necessary. In other words:
- if possible, use owl:Ontology/foaf:Document; otherwise,
- use reification for what cannot be expressed by using

Again, these are only tentative ideas. Feedback from any reader of the
mailing list will be greatly helpful.

Received on Monday, 26 November 2007 10:58:07 UTC

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