Merge branch 'issue-5' into 'develop-v1.1.2'

Issue 5

Closes #5

See merge request SAREF/saref4ener!4

examples/heatingsystem.ttl

@@ -15,6 +15,13 @@
   dcterms:title "Example heatingsystem"@en ;
   dcterms:description "Example heatingsystem"@en .
 
+time:Instant a owl:Class .
+time:DateTimeInterval a owl:Class .
+time:inXSDDateTime a owl:DatatypeProperty .
+time:hasBeginning a owl:ObjectProperty .
+time:hasEnd a owl:ObjectProperty .
+time:hasDurationDescription a owl:ObjectProperty .
+
 time:Beginning_PowerProfile-1-HS0001
   rdf:type time:Instant ;
   rdfs:label "Beginning Power profile-1-HS0001"^^xsd:string ;