Re: MARC Codes for Forms of Musical Composition

Hello all

Two quick points

1. Overloading or abuse of owl:sameAs in linked data land is a well-known
issue that has been discussed at length, before and beyond the (excellent)
quoted paper. A good account of the debate can be found at
http://ontologydesignpatterns.org/wiki/Community:Overloading_OWL_sameAs
Identity is a tricky issue which is representative of the discrepancy
between the "hard" semantics as declared by standards, and the not-so-hard
and various ones implicitly understood by the users, who tend to hack the
original semantics, either because they do not read the specs, or
misunderstand them, or use classes and properties not exactly meaning what
they want, default of more precise ones. Use and abuse of owl:sameAs is
typivcal of this. It's pretty clear that buying all owl:sameAs links in the
linked data cloud to mean what the OWL specification says it means will
entail zillions of inconsistencies of all kinds, the most obvious being that
things considered as distinct here will be merge there. There is no way to
bring global consistency to this "knowledge soup", what is needed is ways to
sort it through various heuristics.

2. I'm amazed that one would debate about unicity of rdf:type at all. It's
certainly a good practice for the URI publisher to *declare* a single
rdf:type. But based on OWL or RDFS semantics, other types will be entailed
even if they are not declared.

for example, to keep it simple :

:x   rdf:type   foaf:Person   will entail
:x   rdf:type   foaf:Agent    based on   foaf:Person    rdfs:subclassOf
foaf:Agent

other types will be entailed from domain declarations of properties used in
the description etc.

In the open world where the URI is used and re-used, linked to and from,
it's obvious that new types will be acquired by entailments. And to be back
to point 1, in particular applying strictly owl:sameAs semantics will bring
about a bunch of possibly conflicting types.

That said, in an open world, an application will be able to pick in the
descriptions the elements it can consume. If something (someone) is declared
with rdf:type foaf:Person and entailed some way to be also skos:Concept, if
my application is interested in the social aspects of the description for a
social web applications, I will consider only the triples with predicates in
the FOAF namespace, and if your application is interested only by this
resource as an entry in a resource index, using e.g. dcterms:subject or
dcterms:creator, you will pick only the predicates in the SKOS namespace
(prefLabel, altLabel ...)

Bernard


2010/7/6 Young,Jeff (OR) <jyoung@oclc.org>

>  Let me address Ross’ question before attempting to argue that restraint
> to a single rdf:type is good practice.
>
>
>
> Here is the example in question:
>
>
>
> http://purl.org/NET/marccodes/muscomp/sy.rdf
>
>
>
> The owl:sameAs property asserts that these two URIs identify “the same
> thing” (http://www.w3.org/TR/owl-ref/#sameAs-def):
>
>
>
> http://purl.org/NET/marccodes/muscomp/sy#genre
>
> http://dbpedia.org/resource/Symphony
>
>
>
> The 1st URI responds with this statement:
>
>
>
> <http://purl.org/NET/marccodes/muscomp/sy#genre> rdf:type <
> http://purl.org/ontology/mo/Genre>
>
>
>
> The 2nd URI responds with this:
>
>
>
> <http://dbpedia.org/resource/Symphony> rdf:type <
> http://sw.opencyc.org/2008/06/10/concept/Mx4rwSmVfJwpEbGdrcN5Y29ycA>
>
> <http://dbpedia.org/resource/Symphony> rdf:type <
> http://sw.opencyc.org/2008/06/10/concept/Mx4rvcNktpwpEbGdrcN5Y29ycA>
>
>
>
> Other rdf:type and owl:sameAs assertions cascade from there in dbpedia.
>
>
>
> The following document isn’t authoritative, but it discusses some of the
> confusion surrounding owl:sameAs and may also help us sort out the issues:
>
>
>
> http://www.w3.org/2009/12/rdf-ws/papers/ws21.
>
>
>
> Here is a quote:
>
>
>
> “However, *owl:sameAs* does have a particular semantics of individual
> identity, namely that the two individuals are *exactly* the same and so
> share all the same *properties*.” (original emphasis).
>
>
>
> Since rdf:type is a property, I assume that an OWL reasoner should back me
> up in my claim that Ross’ example has multiple rdf:types. I just downloaded
> Pellet and will report on the results once I figure out how to run it.
> Hopefully, it will demonstrate how “share” involving owl:sameAs plays out in
> practice.
>
>
>
> Jeff
>
>
>
>
>
> *From:* rxs@talisplatform.com [mailto:rxs@talisplatform.com] *On Behalf Of
> *Ross Singer
> *Sent:* Monday, July 05, 2010 10:03 PM
> *To:* William Waites
> *Cc:* Young,Jeff (OR); Antoine Isaac; Karen Coyle; public-xg-lld@w3.org;
> List for Working Group on Open Bibliographic Data; public-lld
>
> *Subject:* Re: MARC Codes for Forms of Musical Composition
>
>
>
> My question was more based on the fact that I don't think anything should
> have explicitly set multiple rdf:types in there.
>
>
>
> If so, I'm curious to what they are.
>
>
>
> -Ross.
>
> On Mon, Jul 5, 2010 at 3:35 PM, William Waites <william.waites@okfn.org>
> wrote:
>
> On 10-07-05 10:35, Ross Singer wrote:
> > Jeff, which resources have multiple rdf:types?  Of the muscomps, they
> > should all only be mo:Genre.
>
> I think it is perfectly valid to have multiple types. At the
> very minimum everything is an rdfs:Resource whether
> stated explicitly or not. If something breaks when it is
> explicitly stated because it doesn't like multiple types I
> think that something is itself broken...
>
>
> Cheers,
> -w
>
> --
> William Waites           <william.waites@okfn.org>
> Mob: +44 789 798 9965    Open Knowledge Foundation
> Fax: +44 131 464 4948                Edinburgh, UK
>
> RDF Indexing, Clustering and Inferencing in Python
>                http://ordf.org/
>
>
>



-- 
Bernard Vatant
Senior Consultant
Vocabulary & Data Engineering
Tel:       +33 (0) 971 488 459
Mail:     bernard.vatant@mondeca.com
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