Both RDF and Topic Maps have the concept of relationship.

The RDF is a model of triples, hence relationships are binary. Each of them is represented by a subject, a property and an object. The subject is either a URIref or a blank node, and the object, which is the value of the property, can be a literal, a URIref, or a blank node. Topic Maps defines the concept of association, which is intended to be n-ary (e.g., unary, binary, and so on). Each association has a type and n roles players. [Noy 05] identifies patterns for representing n-ary relations in RDF. While Topic Maps has the concept of role player, each of which may be given a type, RDF has only two roles in relations, subject and object.

There is a special type of relation in Topic Maps named occurence. An occurrence is a relation between a subject and an information resource. The information resource may either be a value inside the topic map or an external information resource. Occurrences correspond to RDF single statements. In TM2RDF the conversion is simple, while in RDF2TM it is an issue to decide how to treat a RDF statement: either as an occurrence or an association.

Revision: r1.3 - 26 Oct 2005 - 16:39 - ValentinaPresutti
RDFTM > RDFTMMappingGuidelines > DiscussionPoints > HandlingRelationships
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