Bug: Missing declarations for uriReferenceNodes's in TTL output

[jamrce]

There are discrepancies between the published UML/documentation and the serialized spec/ies-core.ttl regarding temporal representation properties shown in Time 1 of 2 and Time 2 of 2:

1. ical properties are completely missing: ical:dtstart, ical:dtend, and ical:rrule are defined in the visual models with domains, subProperty definitions, and range data types, but they are absent from the serialized TTL file entirely.
2. Missing rdfs:range on iso8601PeriodRepresentation: While ies_core:iso8601PeriodRepresentation is declared in ies-core.ttl, it is missing its rdfs:range xsd:dateTime statement, despite the diagrams explicitly specifying its values as xsd:dateTime literals.

These omissions cause the machine-readable ontology to diverge from its visual documentation and leave external properties as undeclared references.

Suggested Changes

1. Add missing ical property declarations to spec/ies-core.ttl:

ical:dtstart a rdf:Property ;
    rdfs:domain ies_core:ICalRepresentation ;
    rdfs:range xsd:dateTime ;
    rdfs:subPropertyOf ies_core:attribute . 

ical:dtend a rdf:Property ;
    rdfs:domain ies_core:ICalRepresentation ;
    rdfs:range xsd:dateTime ;
    rdfs:subPropertyOf ies_core:attribute . 

ical:rrule a rdf:Property ;
    rdfs:domain ies_core:ICalRepresentation ;
    rdfs:range xsd:string ;
    rdfs:subPropertyOf ies_core:attribute .

2. Add missing rdfs:range to ies_core:iso8601PeriodRepresentation in spec/ies-core.ttl:

ies_core:iso8601PeriodRepresentation rdfs:range xsd:dateTime .