VF — Meta-model diagram(s) in 7.2 should clarify upfront that VdmlElement is the root class.

VdmElement is the root of the VDML metamodel. However, In the first diagram in Figure 6, VdmElement is shown parallel to MeasurableElement (which is actually a subclass of VdmElement). Over the course of the following diagrams, the reader gets the feeling that VdmElement must be the true root, but it takes until figure 19 that you let the cat out of the bag... While Figure 6 is syntactical legal UML, I suggest to show MeasurableElement as a subclass of VdmElement in Figure 6 to establish clarity about root position of VdmElement from the very beginning.

Show MeasurableElement as a subclass of VdmElement in Figure 6

Show MeasurableElement as a subclass of VdmElement in Figure 6 to establish clarity about root position of VdmElement from the very beginning