ISBN : 978-81-963532-2-3 (E-Book) 1 11 1 2 2 22 Wheree, e,…arethebasic(independent) characteristicsofthe software alreadyestimated,and c,c,d,d,…areconstants.Multivariableestimationmodelsareexpectedtogivemore 1 2 1 2 accurate estimates compared to the single variable models, since a project parameter is typicallyinfluencedbyseveralindependentparameters.Theindependentparametersinfluencethedepe ndentparametertodifferentextents.Thisismodeledbytheconstantsc,c,d,d,…. 1 2 1 2 Valuesoftheseconstantsareusuallydeterminedfromhistoricaldata.TheintermediateCOCOMOmode l canbeconsideredto be an exampleof amultivariable estimationmodel. AnalyticalEstimationTechniques Analyticalestimationtechniquesderivetherequiredresultsstarting withbasicassumptionsregarding the project. Thus, unlike empirical and heuristic techniques, analytical techniques dohave scientific basis. Halstead’s software science is an example of an analytical technique.Halstead’ssoftwaresciencecanbeusedtoderivesomeinterestingresultsstartingwithafew simple assumptions. Halstead’s software science is especially useful for estimating softwaremaintenance efforts.Infact, it outperforms bothempirical and heuristic techniques when usedforpredictingsoftwaremaintenanceefforts. Halstead’sSoftwareScience–AnAnalyticalTechnique Halstead’s software science is an analytical technique to measure size, development effort, anddevelopment cost of software products. Halstead used a few primitive program parameters todevelop the expressions for overall program length, potential minimum value, actual volume,effort,and development time. Fora givenprogram,let: ηbethe numberofuniqueoperators usedinthe program, 1 ηbethe numberofuniqueoperands usedin theprogram, Nbethe totalnumberofoperators usedin theprogram, Nbethe totalnumberofoperands usedin theprogram. 2 1 2 LengthandVocabulary ThelengthofaprogramasdefinedbyHalstead,quantifiestotalusageofalloperatorsandoperandsintheprogr am.Thus,lengthN=N+N.Halstead’sdefinitionofthelengthofthe 1 2 programasthetotalnumberofoperatorsandoperandsroughlyagreeswiththeintuitivenotationofthe program lengthasthe total numberoftokens used in theprogram. Theprogramvocabularyisthenumberofuniqueoperatorsandoperandsusedintheprogram. Thus,program vocabulary η=η+η. 156 Software Engineering Keerthana P, Manasa KN, Ganga D Bengal
162 Publizr Home