Re: SKOS modeling

Thank you very much for your answers! It helped me a lot to understand the
difference between SKOS and OWL.

Regards,
Alessandro


*Alessandro Seganti Ph.D.*

Cognitum Sp. z o.o., *Data Engineer*

mail: a.seganti@cognitum.eu <email@cognitum.eu>, tel: +48 22 250 2541, fax: +48
22 250 28 98

web: *http://www.cognitum.eu/ <http://www.cognitum.eu/>*, fb:
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On Fri, Nov 11, 2016 at 1:36 PM, Armando Stellato <stellato@uniroma2.it>
wrote:

> Hi Alessandro,
>
>
>
> A few facts for your knowledge base ;-)
>
>
>
> 1)      SKOS is not separated from OWL, it is actually an OWL vocabulary
> for developing thesauri, its core elements are defined using OWL constructs
> ;-)
>
> 2)      Your statement “All relations are not “hard” ” is not correct.
> The relations (that you define in a thesaurus) are as “hard” as you decide,
> in that you can use properties belonging to the OWL classes of properties
> (ObjectProperty, DatatypeProperty etc..) and you can define as many axioms
> in your vocabulary (intended to be used in a SKOS thesaurus) as you want.
> Even some of SKOS relations have quite a few logical constraints and/or
> allow to have inference based on the facts made explicit through them
>
> 3)      Simply, SKOS provides a unifying vocabulary for addressing
> specific thesauri elements such as concepts (skos:Concept), terminological
> properties (skos:pref/alt/hiddenlabel) generic/specific
> (skos:broader/narrower) etc… there are reasons (see below) for which OWL
> elements have not been used (e.g. owl:Class, rdfs:subClassOf etc..) to
> represent concepts and hierarchies, and they represent the core rationale
> for the development of SKOS, the rest (notation, collections, ConceptScheme
> etc..) are all things which have been added for further covering thesauri
> modeling needs).
>
> In a nutshell, when you need to index some repository (a document repo, or
> a multimedia repo) you may want to semantically index its content with
> “topics”.
>
> What is a “topic”? is not a owl:Class, because it does not need to
> classify instances, and some topics could actually be objects of the world
> which surely do not make sense to represent as classes. Also, concepts need
> to be valued (for instance, for establishing relationships between them).
>
> So owl individuals would be great for that, except that they need to be
> arranged in a hierarchy, but we do not have a standard property for making
> hierarchies of these topics as rdfs:subClassOf addresses classes (oh! But
> we do not even have a standard class for represent these topics!)
>
> So the answer is SKOS..et voilà!, skos:Concept (for these “topics”) and
> skos:borader/narrower (for the hierarchy) are served!
>
>
>
> If you want a longer explanation, here are a couple of readings (which
> would avoid writing a long email to explain those reasons mentioned above)
>
>
>
> When and why using SKOS, and why OWL was not ok. The article is not
> written with logics guru in mind as the audience, and I guess it can give
> you a reading and save you more questions (hopefully). Sorry for the
> self-citation, it’s just I wrote it (following an invited speech to a
> workshop) exactly with the idea to address that OWL/SKOS question which
> kept being asked (so welcome to the club ;-) )
>
> *Armando Stellato* *Dictionary, Thesaurus or Ontology? Disentangling Our
> Choices in the Semantic Web Jungle, Journal of Integrative Agriculture
> (JIA),* 2012
>
> http://art.uniroma2.it/publications/docs/2012_JIA_
> Dictionary,%20Thesaurus%20or%20Ontology%20Disentangling%
> 20Our%20Choices%20in%20the%20Semantic%20Web%20Jungle.pdf
>
>
>
> …but also a practical experience report in which researchers used an
> ontology (and still needed SKOS or SKOS-bound terms) to index a News
> repository could you give a practical answer
>
> Wouter Van Atteveldt, Nel Ruigrok, Stefan Schlobach, Frank Van Harmelen,
> 2007. Searching the News Using a Rich Ontology with Time-bound Roles to
> Search through Annotated Newspaper Archives.
>
> https://www.semanticscholar.org/paper/Searching-the-News-
> Using-a-Rich-Ontology-with-Time-Atteveldt-Ruigrok/
> 1fbb3770ceec83a062c9158360168ada559cd0d7
>
>
>
> Cheers,
>
>
>
> Armando
>
>
>
>
>
>
>
> *From:* Alessandro Seganti [mailto:alessandro.seganti@gmail.com]
> *Sent:* Thursday, November 10, 2016 9:19 AM
> *To:* Reto Gmür <reto@gmuer.ch>
> *Cc:* semantic-web@w3.org; Alessandro Seganti <a.seganti@cognitum.eu>
> *Subject:* Re: SKOS modeling
>
>
>
> Thank you very much for the answer, I think that now I better understand
> the theory behind it.
>
>
>
> 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?
>
>
>
> 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
>
>
>
>
>
>
>