Re: SKOS modeling

Hi Alessandro

On Thu, 10 Nov 2016, at 09:19, Alessandro Seganti wrote:
> Still I am wondering: once you have a thesaurus written in SKOS in
> place, what do you do with it? You use it for tagging? As all
> relations are written as annotations, you cannot reason on it using
> any OWL profile so the only way to get all the broader concepts is to
> make SPARQL queries. What if you want to get the broader concept of a
> broader concept? You translate the SKOS ontology to an OWL ontology?

Well for once you could use a SPARQL query with a transitive property
path. But you can also achieve it by using RDFS and OWL inference on
your SKOS taxonomy, the broader concept of a broader concept is a
skos:broaderTransitive concept (as skos:broader is a sub-property of
skos:broaderTransitive and skos:broaderTransitive is an isntance of
owl:TransitiveProperty).

Reto

>
> I think that my point here is that while SKOS seems easier to use
> because all relations are not "hard", it seems to me of less practical
> use of an RDF/OWL ontology but again I am not a SKOS expert so I
> probably just don't understand it :)
>
>
> Alessandro
>
>
>
> 2016-11-09 18:00 GMT+01:00 Reto Gmür <reto@gmuer.ch>:
>> __
>> Hi Alessandro
>>
>>
>>
>> On Wed, 9 Nov 2016, at 15:36, Alessandro Seganti wrote:
>>> Hi everyone,
>>> after some years working with semantic technologies, I am still not
>>> 100% sure I understand what SKOS is used for.
>>>
>>> To my understanding, SKOS should be used to model relations between
>>> entities that are not certain so instead of modeling it as "is a" we
>>> say that it is "broader than" or things like this.
>>
>> No, it's not about certainty. A SKOS concept may be an owl:Class in
>> which case a super-class would probably be a broader concept.
>>
>>
>>>
>>> If this is true, then I don't understand why I see many people
>>> building taxonomy trees using SKOS relations. Is there some
>>> confusion around or maybe I am missing something?
>>
>> There are certainly many cases where you could use either SKOS or OWL
>> or use them together. The main difference is that OWL classes can
>> have and typically have instances while SKOS concepts cannot be
>> instantiated (unless they are also classes).
>>
>>
>>>
>>> Also could you give me an example where it is better to use SKOS
>>> than to use "is a" relationships?
>>
>>
>> If your data describes different individual dogs you might have
>> various classes for the different breeds of dogs, there probably are
>> some sub-class relations between those classes. Each individual dog
>> is an instance of one or several of those classes. If however your
>> data is about dog books, these books are obviously not an instance of
>> a particular breed of dog but may have a breed of dog as subject. In
>> this case you would better model the different dog breeds as
>> skos:Concepts rather than as owl:Classes.
>>
>> So to summarize:
>> - if you want to categorize some resources use classes so that the
>>   resources can have meaningful types
>> - if you want to describe your thesaurus or want something a bit more
>>   formalized than tags to annotate your items (to say "this has to do
>>   with") use SKOS
>>
>> Hope this helps.
>>
>>
>> Reto
>>
>>
>>

--
  Reto Gmür
  reto@gmuer.ch