IEEE 982.1:2005 pdf free download – IEEE Standard Dictionary of Measures of the Software Aspects of Dependability
1.1 General
This standard has the following clauses: Clause 1 provides the scope of this standard. Clause 2 provides aset of definitions. Clause 3 through Clause 5 specify new, modified, and existing measures for reliability,respectively. Clause 6 and Clause 7 specify new measures for maintainability and availability , respectively.ln addition，there are three informative annexes.Annex A documents the process that was used todetermine whether a measure in the existing standard should be modified, retained, or deleted; this annexstates the criteria that were used to determine whether a measure should be included in the standard,including new measures.Annex B describes the Software Reliability Engineering Case Study，whichprovides a case study example of how to apply selected measures in Clause 3.Annex C is a glossary ofterms taken from The Authoritative Dictionary of IEEE Standards Terms [B8].’Annex D is a bibliographythat provides additional information about measures in Clause 3 through Clause 7.Table 1 summarizes thecategories of measures.Numerical applications of the measures can be found in the reference(s) that arekeyed to cach measure.
Make a risk assessment.Safety Risk pertains to executing the software of a safety criticalsystem where there is the chance of injury (e.g.,astronaut injury or fatality), damage (e.g.,destruction of the Shuttle), or loss (e.g., loss of the mission), if a serious software failure occursduring a mission.
The amount of total test time t, can be considered a measure of the degree to which softwarereliability goals have been achieved. This is particularly the case for systems like the SpaceShuttle where the software is subjected to continuous and rigorous testing for several years inmultiple facilities,using a variety of operational and training scenarios (e.g., by the contractor inHouston, by NASA in Houston for astronaut training, and by NASA at Cape Canaveral).Totaltest time t, can be viewed as an input to a risk reduction process and r(t) and TAt) as theoutputs,with r。 and 1m as”risk criteria levels” of reliability that control the process. Although itcan be recognized that total test time is not the only consideration in developing test strategiesand that there are other important factors，like the consequences for reliability and cost,inselecting test cases (Nikora et al.[B17]), nevertheless, for the foregoing reasons,total test timehas been found to be strongly positively correlated with reliability growth for the Space Shuttle(Musa [B14]).
Equation(B.1) is plotted in Figure B.3 as a function of t, for rc= 1, for OID, where positive,zero，and negative values correspond to r(t) > re,rt)= re,and r(t)< rc, respectively. InFigure B.3 , these values correspond to the following regions: CRITICAL (i.e., above the X-axis,predicted remaining failures are greater than the specified value);NEUTRAL (i.e., on the X-axis,predicted remaining failures are equal to the specified value); and DESIRED (i.e., belowthe X-axis, predicted remaining failures are less than the specified value, which could representa “safe”threshold or, in the Shuttle example, an“error-free”condition boundary). This graph isfor the Shuttle Operational Increment OID (with many years of shelf life): a software systemcomprising modules and configured from a series of builds to meet Shuttle mission functionalrequirements. In this example it can be seen that at approximately tc = 57, the risk transitionsfrom the CRITICAL region to the DESIRED region.