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<H1>Annex H</H1>
<H2>(normative)</H2>
<H1>Safety and Security</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <A NAME="I7291"></A><A NAME="I7292"></A>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: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>Understanding program execution;</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>Reviewing object code;</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>Restricting language constructs whose usage might complicate
the demonstration of program correctness </LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>4.1</FONT></DIV>
<DIV Class="Normal"> <S></S>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. <A NAME="I7293"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> The <FONT FACE="Arial, Helvetica">pragma</FONT>s
Reviewable and Restrictions relate to the other requirements addressed
by this Annex. </DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>1 The <A NAME="I7294"></A>Valid
attribute (see <A HREF="AA-13-9-2.html">13.9.2</A>) is also useful in
addressing these needs, to avoid problems that could otherwise arise
from scalars that have values outside their declared range constraints.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>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''.</FONT></DIV>
<H4 ALIGN=CENTER>Extensions to Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>6.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I7295"></A>This Annex
is new to Ada 95. </FONT></DIV>
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