Designing, implementing and maintaining software for large systems is a non-trivial exercise and one which is fraught with difficulties. These difficulties relate to the management of the software production process itself, as well as to the size and complexity of the software components. Ada is a mature general-purpose programming language that has been designed to address the needs of large-scale system development, especially in the embedded systems domain. A major aspect of the language, and the one that is described comprehensively in this book, is its support for concurrent and real-time programming.

Ada has evolved over the last thirty years from an object-based concurrent programming language into a flexible concurrent and distributed object-oriented language that is well suited for high-reliability, long-lived applications. It has been particularly successful in high-integrity areas such as air traffic control, space systems, railway signalling, and both the civil and military avionics domains. Ada success is due to a number of factors including the following.

• Hierarchical libraries and other facilities that support large-scale software development.

• Strong compile-time type checking.

• Safe object-oriented programming facilities.

• Language-level support for concurrent programming.

• A coherent approach to real-time systems development.

• High-performance implementations.

• Well-defined subsetting mechanisms, and in particular the SPARK subset for formal verification.

The development and standardisation of Ada have progressed through a number of definitions, the main ones being Ada 83 and Ada 95. Ada 2005 now builds on this success and introduces a relatively small number of language changes to provide:

• Better support for multiple inheritance through the addition of Java-like interfaces.

• Better support for OO style of programming by use of the Object.Operator notation.

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