(4)Unit 2《信息管理与信息系统专业英语》MIS2

《信息管理与信息系统专业英语》Unit3—IntroductiontoMIS,ERP&SC--PartI(MIS)《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI--MISInthissession,wewillcoverthefollowingparts:InformationandInformationEntropy1.VocabularySummary2.Basicconcept3.Formaldefinitions《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyVocabularySummaryInformationentropy/informationtheory/probabilitydistribution/plus/subtract(deduce)/multiply/divide/square(square-root)/cube(cube-root)/formula/function/expressionnth-power/nth-root《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyVocabularySummary/positivenumber/negativenumber/real-number/imaginarynumber/Decimal/fraction/remainder/integernon-lossycompressiondiscretemathematic/highermathematic/probabilitytheory/《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyVocabularySummarygeometry/statistics/linearalgebra/operationresearchN-aryentropyFirst-order《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI--MIS马上要举行世界杯赛了。大家都很关心谁会是冠军。假如我错过了看世界杯，赛后我问一个知道比赛结果的观众“哪支球队是冠军”？他不愿意直接告诉我，而要让我猜，并且我每猜一次，他要收一元钱才肯告诉我是否猜对了，那么我需要付给他多少钱才能知道谁是冠军呢?《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI--MIS我可以把球队编上号，从1到32，然后提问：“冠军的球队在1-16号中吗?”假如他告诉我猜对了，我会接着问：“冠军在1-8号中吗?”假如他告诉我猜错了，我自然知道冠军队在9-16中。这样只需要五次，我就能知道哪支球队是冠军。所以，谁是世界杯冠军这条消息的信息量只值五块钱。《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyEntropyisaconceptinthermodynamics(热力学)(seethermodynamicentropy),statisticalmechanics(统计力学)andinformationtheory.Theconceptsofinformationandentropyhavedeeplinkswithoneanother(eachother),althoughittookmanyyearsforthedevelopmentofthetheoriesofstatisticalmechanicsandinformationtheorytomakethisapparent(easilyseenorunder-stood).Thisarticleisaboutinformationentropy,theinformation-theoreticformulation(形成)ofentropy《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyBasicconceptThebasicconceptofentropyininformationtheorydescribeshowmuchrandomness(无序性，随机性)inasignalorinarandomevent.Analternativewaytounderstandthisistotalkabouthowmuchinformationiscarriedbythesignal.《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyAsanexampleconsidersomeEnglishtext,encodedasastringofletters,spaces(空格)andpunctuation(sooursignalisastringofcharacters).Sincesomecharactersarenotverylikely(probable)(e.g.”z”)whileothersareverycommon(e.g.“e”)thestringofcharactersisnotreallyasrandomasitmightbe..《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyOntheotherhand,sincewecannotpredictwhatthenextcharacterwillbe,itdoeshavesome“randomness”.Entropyisameasureofthisrandomness,suggestedbyClaudeE.Shannoninhis1949paper--AMathematicalTheoryofcommunication.《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyBasicconceptShannonderives(obtain)hisdefinitionofentropyfromthefollowingthreeassumptionthat:(1)Themeasureshouldbeproportional(continuous)--i.e.changingthevalueofoneoftheprobabilities(概率)byaverysmallamountshouldonlychangetheentropybyasmallamount.《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyBasicconcept(2)Ifalltheoutcomes(lettersintheexampleabove)areequallylikely--thenincreasingthenumberoflettersshouldalwaysincreasetheentropy.(3)Weshouldbeabletomakethechoice(inourexampleofaletter)intwosteps,inwhichcasetheentropyofthefinalresultshouldbeaweighted(权重的)sumoftheentropiesatthetwosteps.《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyFormaldefinitionsClaudeE.Shannondefinesentropyinterms(words)ofadiscreterandomeventx,withpossiblestatesfrom1tonasThatis,theentropyoftheeventxisthesum,overallpossibleoutcomesiofx,oftheproductofprobabilityofoutcomeitimesthelogoftheprobabilityofi.)(log)())(1(log)(2121iPipipipxHnini《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyFormaldefinitionsWecanalsoapplythistoageneralprobabilitydistribution,ratherthanadiscrete-valuedevent.ShannonshowsthatanydefinitionofentropysatisfyinghisassumptionwillbeoftheformwhereKisaconstant(andisreallyjustachoiceofmeasurementunits).niiPipK12)(log)(《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyFormaldefinitionsShannondefinedameasureofentropythat,whenappliedtoaninformationsource,coulddeterminetheminimumchannelcapacity(最小信道容量)requiredtoreliablytransmitthesourceasencodedbinarydigits.Theformulacanbederivedbycalculatingthemathematicalexpectation(数学期望值)oftheamountofinformationcontainedinadigitfromtheinformationsource.)2121log.......log(nnppppH《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyFormaldefinitionsShannon’sentropymeasurecametobetakenasameasureoftheuncertaintyabouttherealizationofarandomvariable.Itthusservedas(充当)aproxy(代理)capturing(obtain)theconceptofinformationcontainedinamessageasopposedto(而不是)theportion(apart)ofthemessagethatisstrictlydetermined(hencepredictable)byinherent(固有的)structures(结构)..《SQLServer数据库管理与开发》安徽财贸职业学院计算机系PartI—MIS--informationandinformationentropyFormaldefinitionsForexample,redundancyinLanguagestructureorstatistical