SKOS ISSUE-26 Relations between Labels: "SimpleExtension" Proposal
This is a proposal for resolution of [http://www.w3.org/2006/07/SWD/track/issues/26 SKOS ISSUE-26]. See also IssuesProcess.
Resolution of this issue should enable us to satisfy candidate requirement [http://www.w3.org/TR/2007/WD-skos-ucr-20070516/#R-RelationshipsBetweenLabels R-RelationshipsBetweenLabels] (see the [http://www.w3.org/TR/skos-ucr/#Candidate SKOS Use Cases and Requirements] document).
0. Summary
The proposal extends SKOS with the possibility to define a lexical label of a SKOS concept as a resource, such that statements can be made about it. To this end we introduce the class skos:Label plus the corresponding properties (pref, alt, hidden) which link a concept to a label resource. The property skos:labelRelation can be used to express relations between labels. Applications will typically specialize this to define particular label relations. The proposal ensures OWL DL compatibility.
1. Vocabulary
The proposal introduces the following new vocabulary:
skos:Label |
|
skos:prefLabelResource |
skos:altLabelResource |
skos:hiddenLabelResource |
|
skos:labelRelation |
The <x>LabelResource properties are the counterparts of the <x>Label properties and point to a resource instead of a literal.
No vocabulary is deprecated by this proposal.
2. Axiomatic Triples
RDF statements:
skos:Label rdf:type rdfs:Class. skos:prefLabelResource rdf:type rdf:Property. skos:prefLabelResource rdfs:domain skos:Concept. skos:prefLabelResource rdfs:range skos:Label. skos:altLabelResource rdf:type rdf:Property. skos:altLabelResource rdfs:domain skos:Concept. skos:altLabelResource rdfs:range skos:Label. skos:hiddenLabelResource rdf:type rdf:Property. skos:hiddenLabelResource rdffs:domain skos:Concept. skos:hiddenLabelResource rdfs:range skos:Label. skos:labelRelation rdf:type rdf:Property. skos:labelRelation rdfs:domain skos:Label. skos:labelRelation rdfs:range skos:Label.
OWL statements:
skos:Label rdf:type owl:Class;
rdfs:subClassOf [a owl:Restriction
owl:onProperty rdfs:label;
owl:cardinality "1"^^xsd:nonNegativeInteger ].
skos:prefLabelResource rdf:type owl:ObjectProperty.
skos:altLabelResource rdf:type owl:ObjectProperty.
skos:hiddenLabelResource rdf:type owl:ObjectProperty.
skos:labelRelation rdf:type owl:ObjectProperty.3. Semantic Conditions
- In case of multiple prefLabelResource triples with the same subject (a skos:Concept) each object (a skos:Label) should have a unique language tag for its rdfs:label value.
- A skos:Concept must be the subject of at least one one skos:prefLabel or skos:prefLabelR triple. NOTE: there seems to be no reason to forbid mixing of label and class approach. So the "or" is not an exclusive or.
- There is a many-to-one relation between instances of skos:Label and particular rdfs:label values. NOTE: typically it does not make much sense to hve multiple skoks:label instances pointing to the same plain literal within one particular vocabulary; on a Web scale the many-to-one is the only realistic option.
4. Consistent Examples
EXAMPLE 1
The example below defines three labels for a concept, where one label is defined as the acronym of another label.
ex:who rdf:type skos:Concept; skos:prefLabelResource ex:who1; skos:prefLabelResource ex:who2; skos:altLabelResource ex:wh03. ex:who1 rdf:type skos:Label; rdfs:label "World Health Organization"@en-us. ex:who2 rdf:type skos:Label; rdfs:label "Wereldgezondheidsorganisatie"@nl. ex:who3 rdf:type skos:Label; rdfs:label "WHO"@en. ex:acronymOf rdf:type rdf:Property; rdf:subPropertyOf skos:labelRelation. ex:who3 ex:acronymOf ex:who1.
5. Inconsistent Examples
EXAMPLE 2
ex:who rdf:type skos:Concept; skos:prefLabelResource ex:who1; skos:prefLabelResource ex:who2; ex:who1 rdf:type skos:Label; rdfs:label "World Health Organization"@en. ex:who2 rdf:type skos:Label; rdfs:label "World Health Organisation"@en.
EXAMPLE 3
ex:who rdf:type skos:Concept; skos:prefLabelR ex:who1; skos:prefLabelR ex:who2; ex:who1 rdf:type skos:Label; rdfs:label "World Health Organization". ex:who2 rdf:type skos:Label; rdfs:label "Wereldgezondheidsorganisatie"@nl.
6. Entailment Rules
DISCUSSION: should we have an entailment rule that says something like:
for every conceptLabelR statement (i.e. either prefLabelR, altLabelR or hiddenLabelR) tools are allowed to assert a <x>Label triple for each of the rdfs:label statements of the object of the conceptLabelR statement. |
So from example 1, applications may derive the following additional triples:
ex:who skos:prefLabel "World Health Organization"@en-us; skos:prefLabel "Wereldgezondheidsorganisatie"@nl; skos:altLabel "WHO"@en.
DISCUSSION: should the inverse also be true? E.g should applications be allowed to derive the following:
ex:who
skos:prefLabel "World Health Organization"@en-us;
skos:prefLabel "Wereldgezondheidsorganisatie"@nl;
skos:altLabel "WHO"@en.entails |
ex:who
skos:prefLabelR [a skos:Label
rdfs:label "World Health Organization"@en-us];
skos:prefLabelR [a skos:Label
rdfs:label "Wereldgezondheidsorganisatie"@nl];
skos:altLabelR [a skos:Label
rdfs:label "WHO"@en].NOTE: the difference with example 1 is here that the instances of skos:Label are represented as blank nodes.
7. Syntactic Constraints
@@todo
8. Discussion
The objective of this proposal is to allow label relations, while preserving compatibility with the label-as-literal approach. The main alternative would be to drop the semantic constraint on the <x>Label properties to be an owl:DatatypeProperty. This would make the following example consistent:
ex:who rdf:type skos:Concept; skos:prefLabel ex:who1. ex:who1 rdf:type skos:Label; rdfs:label "World Health Organization"@en-us.
even in combination with:
ex:who skos:prefLabel "World Health Organization"@en-us;
One can view this as the MinimalFix proposal but has two disadvantages:
ambiguity wrt the range of the skos:<x>Label properties
- incompatibility with OWL DL, as it is not possible to define the label properties as either an objector a datatype property.
The SimpleExtension proposal preserves OWL DL compatibility. The entailment rules mentioned under 6 are meant to preserve interoperability between vocabularies that use different approaches to represent lexical labels.
[http://lists.w3.org/Archives/Public/public-swd-wg/2007May/0057.html [Discussion Thread]] http://lists.w3.org/Archives/Public/public-swd-wg/2007May/0057.html