The scope of an entity is the range of a program within which an entity
is visible and accessible. Most entities have a scope which is limited to
the program unit in which they are declared, but in special circumstances
some entities can have a scope that is wider than this. The best way to
provide global data is by implementing a MODULE which contains the required
global data declarations and then USE ing it wherever
required
. Global data will be discussed later in Section
5.2.2.