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Best Practice: Be careful with the use of inferencing in RDF Vocabularies

State: Draft

Contact: Nick Crossley

Scope

This Best Practice discusses inappropriate usage of inferencing properties such as rdfs:domain and rdfs:range in RDF vocabularies.

Recommendation

RDFS contains terms such as rdfs:domain and rdfs:range, which go beyond mere vocabulary definition and enter into the world of ontologies. The primary difference between a vocabulary and an ontology is that an ontology includes inference rules which let you infer new information from given information - that is, add new triples to those stated, rather than constrain data to some schema.

For more information on this, read OSLC Resource Shape - A language for defining constraints on Linked Data.

In the light of this knowledge, be careful with the use of inferencing terms in vocabularies - they often do not mean what you might have thought they meant. In particular, do not use rdfs:domain or rdfs:range with multiple values when defining a vocabulary term for a property, since that infers the target of that property is of all mentioned types, not any one of them.

Examples

Here is an example snippet of an RDF vocabulary document:

@prefix oslc:         <http://open-services.net/ns/core#> .
@prefix oslc_qm:      <http://open-services.net/ns/qm#> .
@prefix oslc_rm:      <http://open-services.net/ns/rm#> .
@prefix rdfs:         <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf:          <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

oslc_qm:validatesRequirement
  a rdf:Property ;
  rdfs:isDefinedBy    oslc_qm: ;
  rdfs:label          "validatesRequirement" ;
  rdfs:comment        "Requirement that is validated by the Test Case." ;
  rdfs:range          oslc_rm:Requirement ;
  rdfs:domain         oslc_qm:TestScript, oslc_qm:TestCase ;
  oslc:inverseLabel   "Validated By" .

This states that the target of an oslc_qm:validatesRequirement property is both an oslc_qm:TestScript and an oslc_qm:TestCase - which is not what the author intended. It also implies that any resource using this property may be inferred to be an OSLC requirement - which could prevent reuse of this property for requirements from non-OSLC providers.

In this case, the vocabulary term would be better defined without the use of rdfs:range and rdfs:domain.

The shape for resources using this property should consider use of the oslc:range property to suggest likely target types for the values of the property.

See Also

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