Fixed the definition of measurement.

Closes #36.

ontology/saref4wear.ttl

@@ -647,6 +647,10 @@ saref:Function rdf:type owl:Class ;
 ###  https://saref.etsi.org/core/Measurement
 saref:Measurement rdf:type owl:Class ;
                   rdfs:subClassOf [ rdf:type owl:Restriction ;
+                                    owl:onProperty saref:isMeasurementOf ;
+                                    owl:allValuesFrom saref:FeatureOfInterest
+                                  ] ,
+                                  [ rdf:type owl:Restriction ;
                                     owl:onProperty saref:isMeasuredIn ;
                                     owl:allValuesFrom saref:UnitOfMeasure
                                   ] ,
@@ -671,11 +675,6 @@ saref:Measurement rdf:type owl:Class ;
                                   [ rdf:type owl:Restriction ;
                                     owl:onProperty saref:hasValue ;
                                     owl:cardinality "1"^^xsd:nonNegativeInteger
-                                  ] ,
-                                  [ rdf:type owl:Restriction ;
-                                    owl:onProperty saref:hasValue ;
-                                    owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
-                                    owl:onDataRange xsd:float
                                   ] ;
                   rdfs:comment "Represents the measured value made over a property. It is also linked to the unit of measure in which the value is expressed and the timestamp of the measurement."@en ;
                   rdfs:isDefinedBy saref: ;