This page is a proposal for a section of the ["SKOS/Semantics"] wiki draft. Revised on DateTime().
Module: Semantic (Paradigmatic) Relations
This module defines the formal vocabulary and semantics for the notions of hierarchical and associative semantic (a.k.a. paradigmatic) relations between SKOS conceptual resources.
Hierarchical and associative relations are defined informally in the SKOS Primer.
Vocabulary |
skos:semanticRelation skos:broader skos:narrower skos:related |
Axiomatic Triples |
skos:semanticRelation rdf:type owl:ObjectProperty. BR skos:semanticRelation rdfs:domain skos:Concept. BR skos:semanticRelation rdfs:range skos:Concept. BR skos:broader rdfs:subPropertyOf skos:semanticRelation. BR skos:narrower rdfs:subPropertyOf skos:semanticRelation. BR skos:related rdfs:subPropertyOf skos:semanticRelation. BR skos:narrower owl:inverseOf skos:broader. BR skos:related rdf:type owl:SymmetricProperty. |
skos:broader and skos:narrower denote inverse aspects of the hierarchical relation between SKOS conceptual resources. There are no further semantic conditions on the interpretation of skos:broader and skos:narrower.
The choice not to enforce any further constraints on the interpretation of skos:broader and skos:narrower has been made to allow for alternative reasoning mechanisms to be employed, especially where reasoning is used to drive different query expansion algorithms in information retrieval systems.
This means that skos:broader MAY be interpreted as a transitive property.
Alternatively, skos:broader MAY be interpreted as intransitive. This might be required by more advanced query expansion algorithms, for example, where the number of steps or "semantic distance" between two conceptual resources is an important factor in predicting the relevance of a search result.
This also means that skos:broader MAY be interpreted as a reflexive property (every conceptual resource is broader than itself). This would necessarily follow from asserting that rdfs:subClassOf is a sub-property of skos:broader (see also [@@TODO SKOS+OWL Patterns]).
Alternatively, skos:broader MAY be interpreted as irreflexive (a conceptual resource cannot be broader than itself). This would be more consistent with typical thesaurus or taxonomy-based information retrieval systems, where a hierchical relation between a conceptual resource and itself is usually interpreted as an error.
The transitive closure of skos:broader MAY be interpreted as irreflexive. In other words, a cycle in the hierarchical relation MAY be treated as an error.
skos:related denotes the associative relation between SKOS conceptual resources.
skos:related MUST be interpreted as disjoint with the transitive closure of skos:broader. In other words, an instance of the associative relation cannot also be considered an instance of the hierarchical relation under any circumstances.
This means that the following graphs are each inconsistent:
ex:a skos:broader ex:b. ex:a skos:related ex:b.
...
ex:a skos:narrower ex:b. ex:a skos:related ex:b.
...
ex:a skos:broader ex:b. ex:b skos:broader ex:c. ex:a skos:related ex:c.
...
ex:a skos:narrower ex:b. ex:b skos:narrower ex:c. ex:a skos:related ex:c.
Note finally that skos:related is a symmetric property. This does not mean, however, that sub-properties of skos:related must also be symmetric.