Hi Matthias,
But are "data objects" not just another layer of abstraction? RDF/OWL
gives us the possibility to use URIs and ontologies to describe the
things we are interested in (districts, people, protein sequences)
without taking detours through thinking in terms of documents, data
sets, conceptualisation and other abstractions. When we say that
<http://example1.org/john_doe> owl:sameAs
<http://example2.org/john_doe>, this is a statement about an object in
reality, and not a data object (and, of course, not about a document
either). Maybe this is just a matter of semantics, and with "data
objects" you were actually referring to these objects in reality. For
me, the term "data" is strongly associated with artefacts in our
computer systems, and not objects in reality.
I don't think I agree here. In my sense, all resources "described" in
RDF are representatitons. There are no thing such as "non-information
resource". Even if the description of a "resource" in the URI rfc say
that it can refers to actual "things", we only have their RDF
representations. So, I do think that subjects and objects resource in
triples are representations of some things, and not the actual things.
But, we have to keep in mind that the Web is a of document (information
resource, web resource, call it what you want) and a way to communicate
these documents. Like in a RDF world, on the web, you can't refers to
"non-information resource", so you can't say that a URI is the URI that
defines some "thing". There is no way to infer that a URL is *not* an
information resource (so, a non-information resource).
About sameAs, see bellow.
We have to do a better job of explaining what Object Identity is about
in the context of the Linekd Data Web, especially as this is an area of
computer science that predates the Web.
I think foundational ontologies such as DOLCE [1] and BFO [2] could be
of great utility for clarifying how identities of objects and classes
are defined. I guess that such 'strict' approaches to ontology
engineering are currently not very popular in the LOD community, but I
think that their value will soon be recognized when the LOD dataset
cloud grows -- and more and more questions about the actual meaning of
'sameAs' and 'equivalentClass' arise. At least, this was the case with
the complex RDF/OWL datasets we are dealing with in the life science
and health care community [3].
Well, what is a Class and what is an Individual of a Class? The line is
gray, and and someone's class will be another person's individual. There
are certainly best practices such as DOLCE and BFO, but these are not
sacred books, and different usecases will have an hard time on them.
How to use equivalentClass and sameAs? I think this is quite simple
(hahaha... well...). Basically:
equivalentClass: say that all individuals of a class A belongs to a
class B, and all the individual of a class B belongs to a class A.
However, this doesn't mean that A and B have the same semantic! (check
the OWL doc for more information).
sameAs: can *only* relates two *individuals*. It means that the two
individuals are exactly the same thing (including their semantic).
So you can just use sameAs on a Class in OWL/Full when the class is not
only a class but also an Individual of another class.
So, as you can notice: what is a Class and what is an individual becomes
even more fuzzy in OWL/Full since a class can *also* be an individual of
another class :)
But since we are in a Web of Representations, there will be errors and
inconsistencies (there are on the Web, and there will be on the Semantic
Web)...
And this is normal: my representation of the World, is not the same as
your Representation of the World.
In a case or another.... the discussion is not close (check on the TAG
mailing list for example ahahah :) )
Take care,
Fred
