Session 5 (450K MS-PowerPoint file) - Software Project Management

1、Software Project ManagementSession 5: Scheduling1TodaySession 4 reviewNetwork FundamentalsGantt ChartsPERT/CPM TechniquesMid-term review2Session 4 ReviewPlanningWBSEstimation(Note: NPV, ROI, etc will be covered later in the term)3WBSTypes: Process, product, hybridFormats: Outline or graphical org ch

2、artHigh-level WBS does not show dependencies or durationsWhat hurts most is whats missingBecomes input to many things, esp. schedule4Estimation“The single most important task of a project: setting realistic expectations. Unrealistic expectations based on inaccurate estimates are the single largest c

3、ause of software failure. Futrell, Shafer, Shafer, “Quality Software Project ManagementSession 4 cont.5EstimationHistory is your best allyEspecially when using LOC, function points, etc.Use multiple methods if possibleThis reduces your riskIf using “experts, use twoGet buy-inRemember: its an iterati

4、ve process!Know your “presentation techniques6EstimationBottom-upMore work to create but more accurateOften with Expert Judgment at the task levelTop-downUsed in the earliest phasesUsually with/as Analogy or Expert JudgmentAnalogyComparison with previous project: formal or informalExpert JudgmentVia

5、 staff members who will do the workMost common technique along w/analogyBest if multiple experts consulted7EstimationParametric MethodsKnow the trade-offs of: LOC & Function PointsFunction PointsBenefit: relatively independent of the technology used to develop the systemWe will re-visit this briefly

6、 later in semester (when discussing “software metrics)Variants: WEBMO (no need to know this for exam)Re-Use EstimationSee QSPM outlineU Calgary8Your Early Phase ProcessesInitial Planning: WhySOW, CharterWhat/How (partial/1st pass)WBSOther planning documents Software Development Plan, Risk Mgmt., Cfg

7、. Mgmt.EstimatingSize (quantity/complexity) and Effort (duration)IteratesSchedulingBegins along with 1st estimatesIterates9SchedulingOnce tasks (from the WBS) and size/effort (from estimation) are known: then schedulePrimary objectivesBest timeLeast costLeast riskSecondary objectivesEvaluation of sc

8、hedule alternativesEffective use of resourcesCommunications10TerminologyPrecedence: A task that must occur before another is said to have precedence of the otherConcurrence:Concurrent tasks are those that can occur at the same time (in parallel)Leads & Lag TimeDelays between activitiesTime required

9、before or after a given task11TerminologyMilestonesHave a duration of zeroIdentify critical points in your scheduleShown as inverted triangle or a diamondOften used at “review or “delivery timesOr at end or beginning of phasesEx: Software Requirements Review (SRR)Ex: User Sign-offCan be tied to cont

10、ract terms12TerminologyExampleMilestones13TerminologySlack & FloatFloat & Slack: synonymous termsFree SlackSlack an activity has before it delays next taskTotal SlackSlack an activity has before delaying whole projectSlack Time TS = TL TETE = earliest time an event can take placeTL = latest date it

11、can occur w/o extending projects completion date14Scheduling TechniquesMathematical AnalysisNetwork DiagramsPERTCPMGERTBar ChartsMilestone ChartGantt Chart15Network DiagramsDeveloped in the 1950sA graphical representation of the tasks necessary to complete a projectVisualizes the flow of tasks & rel

12、ationships16Mathematical AnalysisPERTProgram Evaluation and Review TechniqueCPMCritical Path MethodSometimes treated synonymouslyAll are models using network diagrams17MS-Project Example18Network DiagramsTwo classic formatsAOA: Activity on ArrowAON: Activity on NodeEach task labeled withIdentifier (

13、usually a letter/code)Duration (in std. unit like days)There are other variations of labelingThere is 1 start & 1 end eventTime goes from left to right19Node Formats20Network DiagramsAOA consists ofCircles representing EventsSuch as start or end of a given taskLines representing TasksThing being don

14、e Build UIa.k.a. Arrow Diagramming Method (ADM)AONTasks on NodesNodes can be circles or rectangles (usually latter)Task information written on nodeArrows are dependencies between tasksa.k.a. Precedence Diagramming Method (PDM)21Critical Path“The specific set of sequential tasks upon which the projec

15、t completion date dependsor “the longest full pathAll projects have a Critical PathAccelerating non-critical tasks do not directly shorten the schedule22Critical Path Example23CPMCritical Path MethodThe process for determining and optimizing the critical pathNon-CP tasks can start earlier or later w

16、/o impacting completion dateNote: Critical Path may change to another as you shorten the currentShould be done in conjunction with the you & the functional manager244 Task Dependency TypesMandatory Dependencies“Hard logic dependenciesNature of the work dictates an orderingEx: Coding has to precede t

17、estingEx: UI design precedes UI implementationDiscretionary Dependencies“Soft logic dependenciesDetermined by the project management teamProcess-drivenEx: Discretionary order of creating certain modules254 Task Dependency TypesExternal DependenciesOutside of the project itselfEx: Release of 3rd part

18、y product; contract signoffEx: stakeholders, suppliers, Y2K, year endResource DependenciesTwo task rely on the same resourceEx: You have only one DBA but multiple DB tasks26Task Dependency RelationshipsFinish-to-Start (FS)B cannot start till A finishesA: Construct fence; B: Paint FenceStart-to-Start

19、 (SS)B cannot start till A startsA: Pour foundation; B: Level concreteFinish-to-Finish (FF)B cannot finish till A finishesA: Add wiring; B: Inspect electricalStart-to-Finish (SF)B cannot finish till A starts (rare)27Example Step 128Forward PassTo determine early start (ES) and early finish (EF) time

20、s for each taskWork from left to rightAdding times in each pathRule: when several tasks converge, the ES for the next task is the largest of preceding EF times29Example Step 230Backward PassTo determine the last finish (LF) and last start (LS) timesStart at the end nodeCompute the bottom pair of num

21、bersSubtract duration from connecting nodes earliest start time31Example Step 332Example Step 433Slack & ReserveHow can slack be negative?What does that mean?How can you address that situation?34Slack & Reserve35Network DiagramsAdvantagesShow precedence wellReveal interdependencies not shown in othe

22、r techniquesAbility to calculate critical pathAbility to perform “what if exercisesDisadvantagesDefault model assumes resources are unlimitedYou need to incorporate this yourself (Resource Dependencies) when determining the “real Critical PathDifficult to follow on large projects36PERTProgram Evalua

23、tion and Review TechniqueBased on idea that estimates are uncertainTherefore uses duration rangesAnd the probability of falling to a given rangeUses an “expected value (or weighted average) to determine durationsUse the following methods to calculate the expected durations, then use as input to your

24、 network diagram37PERTStart with 3 estimatesOptimisticWould likely occur 1 time in 20Most likelyModal value of the distributionPessimisticWould be exceeded only one time in 2038PERT FormulaCombined to estimate a task duration39PERT FormulaConfidence Interval can be determinedBased on a standard devi

25、ation of the expected timeUsing a bell curve (normal distribution)For the whole critical path use40PERT ExampleConfidence interval for P2 is 4 times wider than P1 for a given probabilityEx: 68% probability of 9.7 to 11.7 days (P1) vs. 9.5-13.5 days (P2)DescriptionPlanner 1Planner 2m 10d10da9d9db12d2

26、0dPERT time10.16d11.5dStd. Dev.0.5d1.8d41PERTAdvantagesAccounts for uncertaintyDisadvantagesTime and labor intensiveAssumption of unlimited resources is big issueLack of functional ownership of estimatesMostly only used on large, complex projectGet PERT software to calculate it for you42CPM vs. PERT

27、Both use Network DiagramsCPM: deterministicPERT: probabilistic CPM: one estimate, PERT, three estimatesPERT is infrequently used 43Milestone ChartSometimes called a “bar chartsSimple Gantt chartEither showing just highest summary barsOr milestones only44Bar Chart45Gantt Chart46Gantt ChartDisadvantag

28、esDoes not show interdependencies wellDoes not uncertainty of a given activity (as does PERT)AdvantagesEasily understoodEasily created and maintainedNote: Software now shows dependencies among tasks in Gantt chartsIn the “old days Gantt charts did not show these dependencies, bar charts typically do

29、 not47Reducing Project DurationHow can you shorten the schedule?ViaReducing scope (or quality)Adding resourcesConcurrency (perform tasks in parallel)Substitution of activities48Compression TechniquesShorten the overall duration of the projectCrashingLooks at cost and schedule tradeoffsGain greatest

30、compression with least costAdd resources to critical path tasksLimit or reduce requirements (scope)Changing the sequence of tasksFast TrackingOverlapping of phases, activities or tasks that would otherwise be sequentialInvolves some riskMay cause rework49Mythical Man-MonthBook: “The Mythical Man-Mon

31、thAuthor: Fred Brooks“The classic book on the human elements of software engineeringFirst two chapters are full of terrific insight (and quotes)50Mythical Man-Month“Cost varies as product of men and months, progress does not.“Hence the man-month as a unit for measuring the size of job is a dangerous

32、 and deceptive myth51Mythical Man-MonthWhy is software project disaster so common?1. Estimation techniques are poor & assume things will go well (an unvoiced assumption)2. Estimation techniques fallaciously confuse effort with progress, hiding the assumption that men and months are interchangeable3.

33、 Because of estimation uncertainty, manager lack courteous stubbornness4. Schedule progress is poorly monitored5. When schedule slippage is recognized, the natural response is to add manpower. Which, is like dousing a fire with gasoline.52Mythical Man-MonthOptimism“All programmers are optimists1st f

34、alse assumption: “all will go well or “each task takes only as long as it ought to takeThe Fix: Consider the larger probabilitiesCost (overhead) of communication (and training)His formula: n(n-1)/2How long does a 12 month project take?1 person: 1 month2 persons = 7 months (2 man-months extra)3 perso

35、ns = 5 months (e man-months extra)Fix: dont assume adding people will solve the problem53Mythical Man-MonthSequential nature of the process“The bearing of a child takes nine months, no matter how many women are assignedWhat is the most mis-scheduled part of process?Testing (the most linear process)W

36、hy is this particularly bad?Occurs late in process and w/o warningHigher costs: primary and secondaryFix: Allocate more test timeUnderstand task dependencies54Mythical Man-MonthReliance on hunches and guessesWhat is gutless estimating?The myth of additional manpowerBrooks Law“Adding manpower to a la

37、te project makes it later55Mythical Man-MonthQ: “How does a project get to be a year late?A: “One day at a timeStudiesEach task: twice as long as estimatedOnly 50% of work week was programmingFixesNo “fuzzy milestones (get the “true status)Reduce the role of conflictIdentify the “true status56Midter

38、m ReviewNext week: MS-Project introduction45 minutesShort BreakExamYou will have rest of class to completeLikely Format: 15-20 questions, most 5 points each57Review - FundamentalsProjects, programs, productsMcConnells four dimensionsClassic mistakesKnow a set of theseRemember by “typePeople, process

39、, product, technology related58ReviewTrade-offs & constraintsThe triangleCost, Time, Scope (And Quality)PMI processes and knowledge areasProcess groupsOrganizational structuresAdvantages & disadvantages of each form59ReviewClassic project phasesAs covered in class Key documents at each phaseSOW, CharterProject Management PlanIdentify key planning documents60Review - LifecycleMethodologiesTrade-offsBasic Pros & ConsGiven a specific scenario decide what SDLC is most appropriateWaterfall processChallenges