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+Figure 1, using PlantUML markup that is supported by Metanorma, rather than Mermaid that works inline in GitHib and ASCIIdoc.
+
+@startuml
+abstract class ReferenceSystem {
+        dimension "dimension >= 1"
+        locationOfApplicability = 0..1
+        timeOfApplicability = 0..1
+        domainOfApplicability = 0..1
+}
+
+note right of ReferenceSystem
+Note: Has at least one of:
+* SpatialReferenceSystem, or
+* TemporalReferenceSystem
+end note
+
+abstract class SpatialReferenceSystem {
+}
+
+abstract class TemporalReferenceSystem {
+  dimension = 1
+}
+
+note left of TemporalReferenceSystem
+Note: Consists of one only of:
+* TemporalCoordinateReferenceSystem,
+* Calendar, or
+* OrdinalTemporalReferenceSystem
+end note
+
+ReferenceSystem <|-- SpatialReferenceSystem : is a
+ReferenceSystem <|-- TemporalReferenceSystem : is a
+
+class OrdinalTemporalReferenceSystem {
+}
+class TemporalCoordinateReferenceSystem {
+}
+class Calendar {
+}
+class Timeline {
+}
+TemporalReferenceSystem <|-- OrdinalTemporalReferenceSystem : is a
+TemporalReferenceSystem <|-- TemporalCoordinateReferenceSystem : is a
+TemporalReferenceSystem <|-- Calendar : is a
+
+OrdinalTemporalReferenceSystem "1" o-- "(ordered)" Events : consists of
+OrdinalTemporalReferenceSystem "1" o-- "0..1" Epoch : anchored by
+OrdinalTemporalReferenceSystem "1" --> "1..*" Notation : is represented by
+TemporalCoordinateReferenceSystem "1" o-- "1" Epoch : anchored by
+TemporalCoordinateReferenceSystem "1" --> "1..*" Notation : is represented by
+TemporalCoordinateReferenceSystem "1" o-- "1" Timescale : must have
+
+Calendar "1" o-- "0..1" Epoch : anchored by
+Calendar "1" --> "1..*" Notation : is represented by
+Calendar "1" o-- "1" Timeline : has a
+
+Timeline "1" o-- "1..*" Algorithm : defined by
+
+class Timescale {
+  StartCount
+  EndCount
+  arithmetic
+}
+
+Timescale "1" o-- "1" Clock : determined by
+Timescale "1" o-- "1" UnitOfMeasure : has a
+
+class Clock {
+}
+Clock "1" o-- "1..*" Ticks : counts
+class Ticks {
+    }
+
+class UnitOfMeasure {
+  Direction
+}
+
+class Algorithm {
+}
+Algorithm "1" o-- "2..*" Timescale : uses
+
+@enduml