Re: Higher-arity to RDF binary

Hi Jitao,

Formally and technically RDF supports only binary relationships. This is by design and there are good reasons.

Still, one can easily model N-ary relationships as classes (on schema level) or through auxiliary nodes (at instance level). For instance, JobPosition in non-RDF environments is likely to be modeld as N-ary relationship, e.g. 

JobPosition(holder, withinOrganisation, jobTitle, from, to)

In RDFS it could be modeled as a class plus several properties:

my:JobPosition a rdfs:Class .
my:holder a rdfs:Property ; rdfs:domain my:JobPosition ; rdfs:range my:Agent .
my:withinOrganisation a rdfs:Property ; rdfs:domain my:JobPosition ; rdfs:range my:Organisation  .
.....

At instance level it may look like:

myData:Pos1 a my:JobPosition ; my:holder myData:Ivan; my:organisation myData:W3C

In case you prefer not to generate identifiers for the auxiliary instance, which is only there to help you model n-ary relationship, one can use blank nodes.

After all, similar things happenr in the RDBMS world whenever one needs to model many-to-many relationship - you need an auxiliary table.

Cheers,
Naso

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Atanas Kiryakov
Executive Director of Ontotext AD, http://www.ontotext.com
Sirma Group, http://www.sirma.bg
Phone: (+359 2) 974 61 44; Fax: 975 3226
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The function of consciousness is not to create reality, but to apprehend it. 
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  ----- Original Message ----- 
  From: Jitao Yang 
  To: semantic-web@w3.org ; www-rdf-interest@w3.org 
  Sent: Saturday, May 15, 2010 4:10 PM
  Subject: Higher-arity to RDF binary


  Dear all,

  Regarding arity, RDF is binary, 
  are there any good methods for encoding higher-arity relations in a graph?

  Thanks,
  Jitao