ISM 50 - Business Information SystemsLecture 13Instructor: John MusacchioUC Santa CruzNov 4, 2010Announcements2nd Folio Article due today nRead qMesserschmitt Ch 11.1 - 11.2 (325-335)qMesserschmitt Ch 15.1 - 15.2 (415-425)Student TalksArchitecture ExampleExample Concept:ArchitecturenHow do you begin to architect a solution for a problem like this?nBreak it into modules!ArchitectureAirline DataserverHEADQUARTERSHHCHHC ServerAirlineIntranetWireless LinkHHC ArchitectureWhen a module is composed of sub-modules, the architecture is hierarchical. HHC ApplicationPalm OSNetworking InfrastructureUser InterfaceCoordinationWith HHC ServerData ManagementHHC ArchitectureWe are using a layered architecture as well. nAllows reuse of previously built infrastructure.HHC ApplicationPalm OSNetworking InfrastructureUser InterfaceCommunicationWith HHC Serverdata managementGranularity tradeoff.nHow big should we make the modulesqMany simple small onesqOr a few complicated big onesnThis aspect of modularity is called granularity.nWhich is better?HHC ServernAgain, we see layering and hierarchy.nBetween each module we specify an interfaceNetworking InfrastructureWindows OSHHC Server ApplicationCommunicationwith airlinedatabaseComputationof key statisticsCommunicationwith HHCStandard Database queries (SQL) relayed to DBMS via OS and infrastructureData serverDatabaseDBMSStandard Database queries (SQL) from HHC ServerOur architecture makes use of theExisting interface of the airline database,so we dont need to redesign it!A simple interface: from within our HHC Server ArchitecureHHC ApplicationPalm OSNetworking InfrastructureComputationof key statisticsCommunicationwith HHCCommunicationwith airlinedatabaseComputationof key statisticsCompute Mean andVarianceMean,VarianceList of numbersInterfacesInterface specifications are often made precise by using data types.nExample type: floatqA number with a decimal placeqHas a certain allowable range, and precision.Computationof key statisticsN numbers ofFloat type2 Numbers of float type that signify:Mean, VarianceCompute Mean andVarianceMore on Data typesnData passing an interface is often specified in terms of a limited number of standard data typesnData type = range of values and allowable manipulationnData type does not presume a specific representation, to allow heterogeneous platformsqRepresentation must be known when data passes a specific module interfaceExample data typesIntegerqnatural number between -32,767 and +32,768qCould be represented (in many ways) by 16 bitsqsince 2n = 65,536Floatqnumber of the form m*10n/32768, where m is in the range -32,767 to +32,768 and n is in the range -255 to +256qCould be represented by 16+8 = 24 bitsMore data typesCharacterqvalues assuming a-z and A-Z plus space and punctuation marksqcould be represented by 7 or 8 bitsCharacter stringqcollection of n characters, where n is customizableqcould be represented by 7*n bitsCompound data typesProgrammer-defined composition of basic data typesExample:Employee {String name;String address;Integer year_of birth;etc.}InterfacesComputationof key statisticsN numbers ofFloat type2 Numbers of float type that signify:Mean, VarianceCompute Mean andVarianceINTERFACEPARAMETERSRETURNSImplementationComputationof key statisticsCompute Mean andVarianceImplementation 1:Xi, i=1..NMEAN,VARIANCEnOne module should not be concerned with other modules implementationq Separation of concerns.nOne module should see the other only through its interface  implementation details hidden.q AbstractionModule AModule BHIDDEN From Module A!!ImplementationComputationof key statisticsCompute Mean andVarianceImplementation 2:Xi, i=1..NMEAN,VARIANCEnThough different, this implementation is ok too.nWe can choose the implementation details however we want, as long as we comply with the agreed interface.Module AModule BImplementationComputationof key statisticsCompute Mean andVarianceImplementation 1:Xi, i=1..NMEAN,VARIANCEnShould he use it?qNO!!!! Why??nEither A should compute SUM himself, or sit down with B and redesign the interfaceModule AModule BI need to get the sum,Ill just take it from BEncapsulationnThe designer of B might take measures to hide SUM from A so that A is not able to violate the agreed interface.qExample: B does not declare SUM as a global variable.nMaking a modules implementation details inaccessible to other modules is called encapsulation.InterfacesComputationof key statisticsN numbers ofFloat type2 Numbers of float type that signify:Mean, VarianceCompute Mean andVarianceINTERFACEPARAMETERSRETURNSnThis simple interface example allows for only one action of module B. qAction is Compute mean and variance.nOther examples are possible.Module BModule APossible software interfaceaction-1action-2action-3...Menu of actionsAction 1: Compute meanAction 2: Compute varianceAction 3: Compute modeEtc..Example:ProtocolIn addition to atomic actions, an interface may define protocolsqProtocol == finite sequence of actions required to achieve a higher level functionqOne action can be shared by multiple protocolsqMultiple modules may participate in a protocolProtocol ExampleHHC ServerHHCHello: Im the gate 32 serverHello: Im the HHC of Airplane#1234Tell me about the passengers of my next flight(Might be passedAs an array of a compound data type passenger, which in turn is composed of standard types like integer, and string)Return PassengerDataPassengers notedThese were the unrulypassengers on last flightAnother Interface Example: Automatic teller machine (ATM)What is the interface between this machine and the customer?Click to edit Master text stylesqSecond levelqThird levelnFourth levelqFifth levelStepsDefine available actionsDefine, for each higher level function, a protocolqSingle action or a finite sequence of actionsInterface building blocksMessage on screen or printedqMenu of actions or returns from an actionqTouch selection of actionKeypadqInput parameters to an actionCard readerqAuthentication, input parametersMoney output slotqReturns moneyAction: authenticationParametersqIdentity (card in slot)qInstitution (card in slot)qPIN (typed on keypad)Internally, it contacts institution and matches against its database, institution noted for all subsequent actions (example of state)ReturnsqScreen message (Invalid PIN or menu of available actions)Action: specify_accountParametersqAccount