Ada packages and the user's conceptual model

Abstract

The private type mechanism of Ada is used to hide the details of the structure of the type from the user (as programmer). Thus, it is possible to build Ada packages that are correct implementations of abstract data types whereby the only operations available on the data type are precisely those made externally available to the user in the visible part of the package specification. To be able to use such a package, the semantics of the operations in the visible part must be unambiguously conveyed to the user. I propose a formal specification and classification of the user of such Ada packages. Associated with each user is an appropriate UCM (user's conceptual model) of the application domain corresponding to which there exists the respective Ada package(s). Such a UCM would incorporate the necessary set of semantics for understanding the visible part of the package(s). In an APSE (Ada programming support environment) it is envisaged that one of the key tools will be an Ada-oriented UIMS (user interface management system) which will perform a function for Ada programmers much like that which a DBMS (data base management system) currently performs for users of a data base. The specification and implementation of the (abstract) data type "complex number" as an Ada package is used as an example.