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Annex H


Safety and Security

   {safety-critical systems} {secure systems} This Annex addresses requirements for systems that are safety critical or have security constraints. It provides facilities and specifies documentation requirements that relate to several needs:
     Execution understandability is supported by pragma Normalize_Scalars, and also by requirements for the implementation to document the effect of a program in the presence of a bounded error or where the language rules leave the effect unspecified. {unspecified [partial]}
   The pragmas Reviewable and Restrictions relate to the other requirements addressed by this Annex.
1  The Valid attribute (see 13.9.2) is also useful in addressing these needs, to avoid problems that could otherwise arise from scalars that have values outside their declared range constraints.
Discussion: The Annex tries to provide high assurance rather than language features. However, it is not possible, in general, to test for high assurance. For any specific language feature, it is possible to demonstrate its presence by a functional test, as in the ACVC. One can also check for the presence of some documentation requirements, but it is not easy to determine objectively that the documentation is ``adequate''.

Extensions to Ada 83

{extensions to Ada 83} This Annex is new to Ada 95.

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