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#>
PREFIX owl:   <http://www.w3.org/2002/07/owl#>
PREFIX swrl:  <http://www.w3.org/2003/11/swrl#>
PREFIX swrlb: <http://www.w3.org/2003/11/swrlb#>
PREFIX vitro: <http://vitro.mannlib.cornell.edu/ns/vitro/0.7#>
PREFIX vivo:  <http://vivo.library.cornell.edu/ns/0.1#>
PREFIX bibo: <http://purl.org/ontology/bibo/>   
PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX event: <http://purl.org/NET/c4dm/event.owl#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX core: <http://vivoweb.org/ontology/core#>

Construct {
     _:edtv a core:DateTimeValue .
     _:edtv core:dateTime ?theEndDate .
     _:edtv core:dateTimePrecision core:yearMonthDayPrecision .
     _:dti a core:DateTimeInterval .
     _:dti core:end _:edtv .
     ?thing core:dateTimeInterval _:dti .
      _:dti core:dateTimeIntervalFor ?thing .
} where {
     ?thing core:endDate ?theEndDate .
     
     Optional {
       ?thing core:startDate ?theStartDate 
     }
     
     FILTER (!bound(?theStartDate))
}