UML Notation Reminder: Is-A
An is-a relationship between 2 classes indicates that one is a subclass of the other - that any object belonging to the subclass is also a member of the superclass. The triangle, rather than drawing order, indicates which is the superclass.
All superclasses in the DRM are abstract - they exist only to abstract common characteristics of their subclasses. They are shaded on class diagrams.
Only concrete classes may have actual objects, so only concrete instances appear in instance diagrams.