Ada packages can be organized into hierarchies. A child unit can be declared independently: 😮

root-child.ads

package Root.Child is
  -- package spec goes here
  end Root.Child;

root-child.adb

package body Root.Child is
   -- package body goes here
   end Root.Child;

Here, Root.Child is a child package of Root.

The public part of Root.Child has access to the public part of Root.

The private part of Child has access to the private part of Root, which is one of the main advantages of child packages.

However, there is no visibility relationship between the two bodies.

One common way to use this capability is to define subsystems around a hierarchical naming scheme.

Primitives

Primitive subprograms in Ada are basically the subprograms that are eligible for inheritance/derivation.

A class in C++ or Java corresponds to a tagged type in Ada.