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Re: ISSUE-26: SimpleExtension proposal

From: Daniel Rubin <rubin@med.stanford.edu>
Date: Thu, 31 May 2007 09:47:15 -0700
Message-Id: <>
To: Antoine Isaac <aisaac@few.vu.nl>
Cc: SWD WG <public-swd-wg@w3.org>

At 06:28 AM 5/30/2007, Antoine Isaac wrote:

>Hi Daniel,
>[To others: just say if this starts getting boring and/or completely wrong]
>>>>In the RadLex use case, for example, "terms" are entities in 
>>>>reality, such as blood vessels. These are linked together via 
>>>>relations such as "part-of" and "continuous-with".  It would be 
>>>>better for these things to be called "Entity" instead of 
>>>>"Term".  I think "Entity" would be consistent with terms and things in reality.
>>>I think your "entity" proposal, I fear this is too 
>>>ontology-oriented. SKOS exists to model knowledge organization 
>>>schemes, as very specific intellectual constructs made of concepts 
>>>(i.e. instances of skos:Concept), not entities in the world 
>>>themselves. For this real world things, ontologies should be used, 
>>>containing instances of owl:Class or rdfs:Class (notice that OWL 
>>>features an owl:Thing that pretty much corresponds to the class of 
>>>your "entities").
>>I thought the goal of SKOS is to "provide a standard way to 
>>represent knowledge organization systems." Ontologies certainly 
>>fall under that umbrella. Some of the SKOS model is certainly very 
>>relevant to people building ontologies.
>Indeed. But assuming that a skos:Concept in a KOS actually denotes 
>entities in the world in a formal way - i.e. making it a class - is 
>an extra interpretation of your concepts.
>For a clearer account on this things just have a look at 
>http://www.w3.org/TR/swbp-skos-core-guide/#secmodellingrdf which 
>tries to explain this distinction.

Perhaps it would be helpful if you provided the formal definition of 
"Concept." Is this the same thing as a "Term?" Clearly, there is a 
difference between actual things and the way we talk about things.

>Notice however that if there is a modeling distinction, there is no 
>exclusion. You can have skos:Concepts (my:Car rdf:type skos:Concept) 
>that are also RDFS/OWL classes (ex:Car rdf:type rdfs:Class) so that 
>you can create 'objects' which are classified under it 
>(ex:danielsCar rdf:type ex:car). This would be needed by a range of 
>applications (including RadLex) that require using SKOS features to 
>define conceptual entities that are actually classes in ontologies.

I'm confused by this statement. You say you can have skos:Concepts 
(my:Car rdf:type skos:Concept) that are also RDFS/OWL classes (ex:Car 
rdf:type rdfs:Class)--how can it be that a concept is also something 
tangible such as a car?

>Notice that such a trick is needed because SKOS does not make any 
>assumption on the interpretations of instances of skos:Concept. 
>Before you say it is an RDFS/OWL class (eventually just by creating 
>an instance of it using rdf:type), your ex:Car is not expected to 
>denote a set of "entities" in a "real" world (i.e. a concrete one, 
>made of all kind of things like blood vessels and cars).

I'm trying to understand this in terms of the relationship between 
skos:Concept and RDFS/OWL class. Are you saying that it is possible 
to say that owl:Class is-a skos:Concept?

>>>This is actually another point for not introducing "term" in SKOS, 
>>>but something else, with much less "conceptual" load, like it was 
>>>for "label". It would be too confusing, otherwise, with half  (or 
>>>even more) of the existing thesauri assuming a "term-based" approach.
>>I think I need to understand better exactly *what* SKOS is 
>>describing--names of things? The things themselves? Both? Something 
>>else?  To me, "term" is the name for something. "Concept" is 
>>something that is someone's head. "Entity" is something that exists 
>>in reality. There are certainly communities who need to describe 
>>things, names of things, and both (in the case of RadLex). Ideally, 
>>SKOS should be able to be useful to these communities.
>I hope that my previous point helps. I think we are not that far way 
>from each other anyway.
>So to sum up my understanding, SKOS is meant to describe concepts, 
>as "something in someone's head".
>The point is that a concept can just stay in someone's head, or 
>at  the level of a (set of) manifestation in one language. This is 
>the level at which a skos:Concept would appear in a library, let's 
>say. They know what a car is (skos:definition "a car is something 
>that has four wheels, etc."), what it is semantically related to 
>(skos:broader ex:TransportMeans) and what labels are used to name it 
>in language (skos:prefLabel "car"@en). But their "world" do not 
>contain any concrete car.

It's fine if skos wants to stay restricted to how people "talk about 
things", but there needs to be a formal way of relating that to 
ontologies that contain classes representing the things themselves 
and that also want to talk about how they are named. That's what's 
going on in RadLex.

>Then, if you have another world interested in car "entities" you 
>would have to make your car an RDFS/OWL class, that denote set of 
>concrete car entities (ex:danielsCar rdf:type ex:Car). But here we 
>enter the field of ontology engineering, and we don't want SKOS to 
>be redundant with RDFS/OWL

But we need to be able to give ontology people a way to say in their 
ontology that their entities are named things, which is where skos 
comes in. It would not be semantically correct to do this by making 
owl Classes subclasses of skos:Concept.

>>>Do you see my point(s), Daniel? And do you think the 
>>>"lexicalization" I've proposed in another mail to replace "term" 
>>>(making it closer to the intuition behind "label") would make 
>>>things less ambiguous?
>>I don't recall what you want to replace "term" with.
>"lexicalization". It's so natural that you have not spotted it in my 
>sentence. Good sign ;-)
Received on Thursday, 31 May 2007 16:47:29 UTC

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