prism:publicationDate leaf node

@prefix dc: <http://purl.org/dc/elements/1.1/> .
@prefix dcterms: <http://purl.org/dc/terms/> .
@prefix frbr: <http://purl.org/vocab/frbr/core#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix prism: <http://prismstandard.org/namespaces/basic/2.0/> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .

prism:publicationDate a owl:DatatypeProperty,
        owl:FunctionalProperty ;
    rdfs:label "has publication date"@en ;
    dc:description """The date on which a document or entity is published.
The date can be expressed in three different formats:
- yyyy-mm-dd (i.e., xsd:date)
- yyyy-mm (i.e., xsd:gYearMonth)
- yyyy (i.e., xsd:gYear)"""@en ;
    rdfs:comment "The date on which a resource is published or disclosed."@en ;
    rdfs:domain frbr:Endeavour ;
    rdfs:range [ a rdfs:Datatype ;
            owl:unionOf ( xsd:date xsd:gYear xsd:gYearMonth ) ] ;
    rdfs:subPropertyOf dcterms:issued .