Kiến trúc máy tính và hợp ngữ - Chapter 5: Functional modeling

Chapter 5:Functional ModelingObjectivesUnderstand the rules and style guidelines for activity diagrams.Understand the rules and style guidelines for use cases and use-case diagrams.Understand the process used to create use cases and use-case diagramsBe able to create functional models using activity diagrams, use cases, and use-case diagrams.BUSINESS PROCESS MODELING WITHACTIVITY DIAGRAMSBusiness Process ModelingBusiness process models describe the activities that collectively support a business processA very powerful tool for communicating the analyst’s current understanding of the requirements with the userActivity diagrams are used to model the behavior in a business processActivity Diagram SyntaxAction or ActivityRepresents action or set of actionsControl FlowShows sequence of executionInitial NodeThe beginning of a set of actionsFinal NodeStops all flows in an activityDecision NodeRepresents a test conditionSample Activity DiagramGuidelines for Activity DiagramsSet the scope of the activity being modeledIdentify the activities, control flows, and object flows that occur between the activitiesIdentify any decisions that are part of the process being modeledIdentify potential parallelism in the processDraw the activity diagramUSE-CASE DESCRIPTIONSUse CasesA use case illustrates the activities that are performed by users of a system.Describe basic functions of the systemWhat the user can doHow the system respondsUse cases are building blocks for continued design activities.Types of Use CasesPurposeAmount of informationOverviewDetailEssentialHigh-level overview of issues essential to understanding required functionalityDetailed description of issues essential to understanding required functionalityRealHigh-level overview of a specific set of steps performed on the real system once implementedDetailed description of a specific set of steps performed on the real system once implementedUse Case Elements: OverviewNameID NumberTypePrimary ActorBrief DescriptionImportance LevelStakeholder(s)Trigger(s)Use Case Elements: RelationshipsAssociationdocuments the communication between the use case and the actors that use the use caseExtendrepresents the extension of the functionality of the use case to incorporate optional behaviorIncludeshows the mandatory inclusion of another use caseGeneralizationallows use cases to support inheritanceUse Case Elements: FlowsNormal Flowsinclude only those steps that normally are executed in a use caseSub-Flowsthe normal flow of events decomposed to keep the normal flow of events as simple as possibleAlternate or Exceptional Flowsflows that do happen but are not considered to be the normUse Case Writing GuidelinesWrite in the form of subject-verb-direct objectMake sure it is clear who the initiator of the step isWrite from independent observer’s perspectiveWrite at about the same level of abstractionEnsure the use case has a sensible set of stepsApply the KISS principle liberally.Write repeating instructions after the set of steps to be repeatedUSE-CASE DIAGRAMSUse Case Diagram SyntaxActorperson or system that derives benefit from and is external to the subjectUse CaseRepresents a major piece of system functionalityAssociation RelationshipInclude RelationshipExtend RelationshipGeneralization Relationship>>Sample Use CaseCREATING USE-CASE DESCRIPTIONSAND USE-CASE DIAGRAMSIdentify the Major Use CasesReview the activity diagramFind the subject’s boundariesIdentify the primary actors and their goalsIdentify and write the overviews of the major use cases for the aboveCarefully review the current use cases. Revise as neededExtend the Major Use CasesChoose one of the use cases to expandStart filling in the details of the chosen use caseWrite the normal flow of events of the use caseIf the normal flow of events is too complex or long, decompose into sub flowsList the possible alternate or exceptional flowsFor each alternate or exceptional flow, list how the actor and/or system should reactConfirm the Major Use CasesCarefully review the current set of use cases. Revise as neededStart at the top againCreate the Use Case DiagramDraw the subject boundaryPlace the use cases on the diagramPlace the actors on the diagramDraw the associationsREFINING PROJECT SIZE AND EFFORTESTIMATION USING USE-CASE POINTSUse-Case PointsA size and effort estimation technique that was developed around use casesBetter for OOSAD projects than function pointsRequires at a minimum:The set of essential use casesThe use case diagramAll actors and use cases classified as simple, average, or complexActor & Use Case Weighting TablesActor TypeDescriptionWeighting FactorSimpleExternal System with well-defined API1AverageExternal System using a protocol-based 2interface, e.g., HTTP, TCT/IP, or a database2ComplexHuman3Use-Case TypeDescriptionWeighting FactorSimple1-3 transactions5Average4-7 transactions10ComplexMore than 7 transactions15Unadjusted Use Case Points (UUCP) = UAW + UUCWUnadjusted Use Case Weighting (UUCW)Unadjusted Actor Weighting (UAW)Technical Complexity FactorsFactor NumberDescriptionWeightT1Distributed system2.0T2Response time or throughput performance objectives1.0T3End-user online efficiency1.0T4Complex internal processing1.0T5Reusability of code1.0T6Easy to install0.5T7Ease of use0.5T8Portability2.0T9Ease of change1.0Technical Complexity Factor (TCF) = 0.6 + (0.01 * TFactor)Environmental FactorsFactor NumberDescriptionWeightE1Familiarity with system development process in use 1.5E2Application experience 0.5E3Object-oriented experience 1.0E4Lead analyst capability 0.5E5Motivation 1.0E6Requirements stability 2.0E7Part time staff-1.0E8Difficulty of programming language-1.0Environmental Factor (EF) = 1.4 + (-0.03 * EFactor)Person-Hours MultiplierIf the sum of (number of Efactors E1 through E6 assigned value 3) ≤ 2PHM = 20Else If the sum of (number of Efactors E1 through E6 assigned value 3) = 3 or 4PHM 28ElseRethink project; it has too high of a risk for failureComputing Use-Case PointsAdjusted Use Case Points (UCP) = UUCP * TCF * ECFEffort in Person Hours = UCP * PHMSummaryBusiness Process Modeling with Activity DiagramsUse-Case DescriptionsUse-Case DiagramsRefining Project Size and Effort Estimation with Use-Case Points