IMSchach8thedChap12v7.docx

IMSchach8thedChap12v7.docx

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IMSchach8thedChap12v7

Chapter12

ClassicalAnalysis

Inthischapter,threeapproachestospecificationarecompared:

formal,semiformal,andinformal.Ifeelthatstudentsshouldbeexposedtoasmanyformalmethodsaspossible.OnewaytointroducetheFSMmaterialtostudentswhohavehadnopriorexposuretoformalmachinesistodescribeamenu-basedproductwithwhichmoststudentsarefamiliar,suchasapopularword-processingpackageonaPC.Pointoutthateachmenucorrespondstoastate,andeachmenuchoicetoaninput.Oncestudentsappreciatethattheyhavebeendealingwithfinitestatemachinesforyears,Section12.7iseasytoteach.

StudentswhohavetakenanoperatingsystemscoursemaywellhavebeenexposedtoPetrinets.Also,thebasicconceptcanbeeasilyunderstoodbymostoftheclasswithoutmucheffortbytheinstructor.IbelievethatSection12.8shouldbecovered,ifonlytoensurethatstudentsareexposedtoPetrinets.However,notallstudentswillbeabletodoProblem12.17.

Ontheotherhand,IteachSections12.9and12.10toonlygraduatestudents.Furthermore,thereisonlyoneprobleminvolvingZattheendofthechapter.

problemsolutions

12.1:

Bothconstraintssuperficiallyappeartobepreciseandscientific,butneithercanbemeasuredortested.Specifically,

（i）Theterm“significantly”isimprecise—significantforwhom:

clientordeveloper?

Also,thisisareasonfordevelopingtheproduct,notaconstraint.

（ii）Theterm“reasonable”isimprecise—reasonableforwhom:

clientordeveloper?

12.2:

Anysuchomissions,contradictions,andambiguitieswillbecarriedoverintothedesignandimplementation.

12.3:

Ambiguities:

Isacloveoraheadofgarlictobeused?

Whatoperationsaretobeperformedthenightbefore?

Everything?

Whichjuiceistobestrained,orangeorlemon?

Whatistobefrozen,thelemonorjustthejuice?

Istheoniontobediced,orjusttheshallots?

Whichmixtureistobeblendedfor10minutes?

Does“blend”mean“mixbyhand”or“useanelectricblender?

”

Howarethelumpstoberemoved,withastrainerorablender?

Thelumpsinthemixturecouldbethemushrooms.

Twomixturesarespecified,thepockwesterisaddedtoonlyoneofthem:

which?

Howcanyoukilla“fresh”pockwester?

Theterms“simmer,”“bite-sized,”and“softtothetouch”areimprecise.

Wecanbroilforanytimefrom1microsecondto3minutes,59seconds.

WhatistobesprinkledwithParmesan—theservingplatter,orthepockwester?

Omissions:

Howlargeisa“largeonion”?

Whatsizecanoforangejuice?

Howlargealemon?

Whatkindofbreadforthecrumbs?

Howmuchflour?

Howmuchmilk?

Howlargearemedium-sizedshallots?

Howlargearemedium-sizedeggplants?

Whatsizepockwester?

Whatsizegarlic?

HowmuchParmesancheese?

Whatsizeeggs?

Thesugarisnotlistedintheingredients.

Norarethemushrooms.

Norarethefrobs.

Whatsizeplatteristobeused?

Contradictions:

Theingredientscallforfrozenorangejuice,therecipecallsforfresh.

Afterthelemonhasbeensqueezedthenightbefore,itisthensupposedtobesliced.

Wearetoldto“stirvigorously,”“slice,”and“inthemeantime”tocoat,dip,andsoon—itisimpossibletodoallthesethingsatonce.

Thefollowingitemsarecertainlyconfusing,buttheyarenotambiguities,omissions,orcontradictions:

Thelemonjuice,eggplant,andgarlicareneverused.

Grillinginaskilletisnotusuallyagoodidea.

Shakingupmushroomswetwithmilkinapaperbagisfraughtwithdifficulties.

Theinstructiontowhisktheeggsshouldprecedetheinstructiontoaddthemtoamixture.

Iftheblendingistobedonewithanelectricblender,10minutesseemstobetoolong.

Therecipecallsforfirstcoatingthemushroomsinflour,andthendippingtheminmilk;thismaybeunorthodox,butthensoismuchoftherestoftherecipe!

Twomixturesarespecified,thepockwesterisaddedtoonlyoneofthem;nothingismentionedregardingwhatistobedonewiththeotherone.

12.4:

Ifactualsalesforthecurrentmontharelessthanthetargetsalesforthecurrentmonth,checkwhetherthepercentagedifferencebetweentheactualsalesandthetargetsalesforthecurrentmonthis5percentormore.Ifso,checkwhethertherearesalesfiguresforthepreviousmonth.Ifso,checkwhetherthepercentagedifferencebetweentheactualsalesandtargetsalesforthecurrentmonthisgreaterthanorequaltohalfofthepercentagedifferencebetweentheactualsalesandtargetsalesforthepreviousmonth.Ifthisthirdconditionalsoholds,printareport.Otherwise,donothing.

12.5:

Foreachshop,theactualsalesforeachmontharecomparedwiththetargetsalesforthatmonth.

Theeffectivenessofagivenshopforagivenmonthisdefinedby

Theshortfallforagivenshopforagivenmonthisdefinedby

Ashopisdeemedtohaveachieveditsobjectiveforthecurrentmonthiftheshortfallforthecurrentmonthislessthanorequalto5%,oriftheshortfallforthecurrentmonthislessthanorequaltohalftheshortfallforthepreviousmonth;inthecaseofJanuary,theshortfallforthepreviousmonthisdeemedtobe0%.

Ifashophasnotachieveditsobjective,areportistobeprinted.

12.6:

Informalspecificationsareeasytouse,andareeasyfortheclienttounderstand.

12.7:

Informalspecificationsareimprecise.Theycanbeambiguous,contradictory,orincomplete.

12.8:

Thefollowingassumptionsaremade:

therearenoservicecharges,noATMwithdrawals.Theonlytransactionsthatareallowedarechecksanddeposits.Allchecksbearanumber.Theuserhasapileofcanceledchecks,andapileofdepositslips.

Figure12.1.Dataflowdiagramfordeterminingwhetherbankstatementiscorrect.

Sortthechecksincheck-numberorder.Foreachcheck,findanentryinthebankstatementthatmatchesthechecknumber.Ifnosuchentryisfound,thestatementisinerror.Otherwise,markthatentry,andverifythattheamountforthatentryisthesameasthatonthecheck.Iftheamountsdonotmatch,thestatementisinerror.

Sortthedepositslipsaccordingtodateofdeposit.Foreachdepositslip,findanentryinthestatementthatmatchesthedateofdepositandtheamountofthedeposit.Markthatentry.Ifnosuchentryisfound,thestatementisinerror.

Afterallchecksanddepositshavebeenprocessed,verifythatallitemsonthestatementhavebeenmarked.Ifnot,thestatementisinerror.

Addtheamountofalldepositstothebeginningbalance,andfromthatsumsubtractthetotalofallthechecks.Iftheresultofthatsubtractionisnotequaltotheendingbalancethenthestatementisinerror,otherwiseitiscorrect.

12.9:

SeeFigure12.1.

12.10:

Thisproductisconcernedwithbooks,borrowers,andlibrarians.Thelibraryhasacollectionofbooksthatborrowersmaycheckoutandsubsequentlyreturn.Eachbookhasauniquebooknumber.Affixedtoeachbookisalabelbearingthatnumberinbar-codeformat.

Eachborrowerhasauniqueborrowernumber.Eachborrowerhasacardbearingthatnumberinbar-codeformatthatisscannedwhentheborrowerchecksoutabook.BorrowersmaydetermineallthebooksbyaparticularauthorinthelibrarycollectionbygoingtoaterminalandenteringA=,allthebookswithaspecifictitlebyenteringT =,orallthebooksinaparticularsubjectareabyenteringS = .

LibrarianscheckoutabookbyenteringCataterminal,scanningtheborrowerbarcode,andscanningthebookbarcode.Ifthebookisnotbeingheldforanotherreader,itisissuedtotheborrower.Whenaborrowerreturnsabook,thelibrarianentersRataterminal,andscansthebookbarcode.Toaddanewbooktothecollection,thelibrarianenters+（plussign）,thenumberofthenewbook,andotherbookdetails.Toremoveabookfromthecollection,thelibrarianenters–（minussign）andentersthebooknumber（bar-codeinputisinappropriate—thebookmayhavebeenstolen）.AlibrariancanputaholdonabookforaborrowerbyenteringH=andscanningtheborrower’sbarcode.[Theneedfortheborrower’snumberwasintentionallyomittedfromtheproblemstatement;studentsshouldnotthoughtlesslyrewritetheproblemstatementinmoreformalterms,butactuallyconsidertheimplicationsofwhattheyarewriting!

]Abookmaynotbeheldifitisalreadybeingheldforanotherborrower.

12.11:

SeeFigure12.2.

12.12:

Step1.DrawDFD.Seepreviousproblem.

Figure12.2.Dataflowdiagramforlibrarycirculation.

Step2.Decidewhatsectionstocomputerize,andhow.ComputerizecompleteproductasshowninDFD,online.DFDdoesnotshowfunctionslikeissuingnewborrowerwithanIDnumberandcard,ormaintainingborrowerdetails.Thesefunctionswerenotincludedinthespecifications,anditisthereforeassumedthattheywillbeperformedmanually.

Step3.Detailsofdataflows.

book_ID

book_number

book_details

book_number

book_bibliographic_details

author

title

subject

other_details

borrower_ID

borrower_number

on_hold_data

borrower_numberifbookisonholdforanotherborrower,else0

Step4.Definelogicofprocesses.

addbook

Placebook_detailsinBOOK_DATA

checkoutbook

Readbook_ID,borrower_ID

Checkthatbookisnotbeingheldforanotherborrower

UpdateBOOK_DATAwithborrower_ID

holdbook

Readbook_ID,borrower_ID

Checkifbookisalreadyonhold

Ifnot,updateBOOK_DATAtoreflectborrower_ID

obtaincataloginformation

Readborrower’squery

SearchBOOK_DATA

Answerborrower’squery

removebook

Readbook_ID

Deletebook_detailsfromBOOK_DATA

returnbook

Readbook_number

UpdateBOOK_DATA