1. Introduction

Ada is a programming language designed in accordance with requirements defined by the United States Department of Defense: the so-called Steelman requirements. Overall, these requirements call for a language with considerable expressive power covering a wide application domain. As a result, the language includes facilities offered by classical languages such as Pascal as well as facilities often found only in specialized languages. Thus the language is a modern algorithmic language with the usual control structures, and with the ability to define types and subprograms. It also serves the need for modularity, whereby data, types, and subprograms can be packaged. It treats modularity in the physical sense as well, with a facility to support separate compilation.

In addition to these aspects, the language covers real-time programming, with facilities to model parallel tasks and to handle exceptions. It also covers systems programming; this requires precise control over the representation of data and access to system-dependent properties. Finally, both application-level and machine-level input-output are defined.