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RDFTM.HandlingUnaryr1.2 - 27 Oct 2005 - 20:07 - ValentinaPresuttitopic end

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Unary relationship

Topic Maps allows to define unary associations. If we want to say in Topic Maps that the "turandot" is an unfinished work we can use a unary association like the following:

unfinished(turandot : work) [LTM syntax]

In RDF we do not have unary assiciations. Typically we model a situation like this by defining the resource "turandot" as instance of a specific set or by using a boolean binary association. The problem is how to translate this kind of assertions from Topic Maps to RDF obtaining roundtripping. The approach for translating unary associations is to use a special class with the semantics of describing a particular characteristic that its instances have.

For the guidance of unary associations translation we define two classes which are disjoint:

  • rdftm:NonEssentialClass, which represents the semantic of unary associations.
  • rdftm:EssentialClass.

The rules for translation are as follows:


  • A class which is rdfs:subClassOf rdftm:NonEssentialClass translates to a Topic Maps unary relation.
  • The resource, which is instance of that class becomes the role player of the corresponding unary relation.


  • A unary relation becomes a class in RDF, which is rdfs:subClassOf rdftm:NonEssentialClass.
  • The topic which is the role player of the unary relation becomes a resource, which is instance of the class created.

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