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                         13.3  APPLICATIONS FOR ADA PACKAGES
	
	Ada is a general-purpose language with considerable power, but it
still does not prevent a programmer from abusing certain features of the
language -- it is definitely possible to write unreadable, unstructured Ada
code.  To avoid this trap, each language construct must be applied in a
purposeful manner.  This is clearly true for Ada packages, since they form
an essential element of any software system.  Ada packages should be
logically small, that is, they should export only a single, small chunk. 
We recommend four different applications for Ada packages, namely:

	named collections of declarations
	
	groups of related program units

	abstract data types

	abstract state machines

	These applications are further characterized by the kinds of
entities they usually export:

	Named collections of declarations
	Export objects and types.
	Do not export other program units.

	Groups of related program units
	Do not export objects and types.
	Export other program units.

	Abstract data types
	Export objects and types.
	Export other program units.
	Do not maintain state information in the body.

	Abstract state machines
	Export objects and types.
	Export other program units.
	Maintain state information in the body.

	Note that these represent the purest form of application:  in
practice, we may find hybrid versions.  The following sections provide a
discussion and examples of each of these general applications.