Estimates by liaoqinmei

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									                   Estimates

Estimates
   Uncertainties
   Unknown
      Project development costs
      Project development schedules
      Team size
      Amount of software to be developed
      Hardware resources
                 Estimates

Estimation techniques
   Historical data
      Stepwise Estimation
   Counting product features
      Functional point Analysis
   Statistical application
   Construction Cost Model COCOMO
                Estimates

Stepwise Estimation
   Divides a large problem into numerous
    smaller problems.
   The basic approach decomposes the
    project into well-defined components, then
    to iterate step-by-step until only small units
    remain, which can be easily estimated.
                Estimates

Stepwise Estimation
   Project Decomposition
      Off-the-shelf components
      Full-experience components
      Partial-experience components
      New development
               Estimates

Estimating New Development
   Prototype methods
   Statistical methods
                            Estimates



              Charter                       Plan
Pre-Launch   Approval       Launch        Approval      Execute


   Size Estimates (Macro)       Task-based Estimates   Project Schedule

        +/- 35% range                +/- 15% range     +/- 10% range
                 Estimates

Sizing techniques /models
   Used to generate high-level effort,
    duration, and cost projections at a point
    when little is known about the project
      Effort Distribution Models (EDM)
      Deliverables-Based Estimates
      Functional Point Estimating Models


   Used for new development mostly
                    Estimates

     EDM
Intial Study (IS)                2
User requirement (UR)            5
Conceptual design (CD)          12
External design (ED)            14
Internal design (ID)            19
Code & unit test (CUT)          26
System/acceptance test (SAT)    17
Instalation (IN)                 3
Post-implementation (PI)         2
                            EDM


     System/accept
     ance test (SAT)                         Conceptual
          17%              Intial Study (IS) design (CD)
   User                           2%            12% External design
requirement                                                 (ED)
   (UR)                                                     14%
    5%
                                                      Instalation (IN)
    Code & unit                                             3%
    test (CUT)              Post-           Internal design
       26%             implementation             (ID)
                             (PI)                 19%
                             2%
                Estimation (EDM)
      Completed Phases            Effort %       Actual hours
        Intial Study (IS)             2              1426
     User requirement (UR)            5              1949
     Conceptual design (CD)          12              4138
                                     19              7513

Future phases                  Effort        Extrapolated effort
External design (ED)                    14            5536
Internal design (ID)                    19            7513
Code & unit test (CUT)                  26           10281
System/acceptance test (SAT)            17            6722
Instalation (IN)                         3            1186
Post-implementation (PI)                 2             791
Total                                   81           32029
                    Estimation (EDM)
Converting effort hours into estimate durations.
       Convert the estimated phase effort hours to work months by
        dividing the total hours by the average production hours per
        month per person.
             6.5 work-hours per day and 17.5 work-days per month
       Determine the Optimal Full-time Equivalent (OFTE) team members
        for each phase by taking the square root of the work months
        computed above
       Compute the estimated phase duration as
             Phase duration = work months / OFTE
       Develop a phase-base Gantt – depict the order of phase execution
        and appropriate phase overlaps and determine the duration
        estimate in terms of work-days, works weeks, or work-months.

    Problems
       Effort for user participation are usually not included
       A full-time PM for a 7 FTE team member. That is one FTE will
        consume 15% of PM’s time.
              Estimation (EDM)



phases    Work month   Team OFTE   Duration months   PM FTE
  (ED)     5536/114       48.6            6.9           1
   (ID)    7513/114       65.9            8.1          1.2
 (CUT)     10281/114      90.2            9.5          1.4
 (SAT)     6722/114        59             7.7          1.1
   (IN)    1186/114       10.4            3.3          0.5
   (PI)     791/114        6.9            2.7          0.4
                      Estimation (EDM)
  0 month         10 months                 20 months                 30 months
       ED
                 ID
                                    CUT
                                                      SAT
                                                                 IN         PI

                              PM Effort
0 month      10 months                    20 months              30 months
  ED
            ID
                                  CUT
                                                 SAT
                                                            IN         PI
          Estimation (EDM)

When to use EDM
   Medium to large projects
   Projects based on a well defined lifecycle
    methodology
   Major enhancements
Size Estimate (Deliverables-based)

 Deliverables-based estimates
    Project description
    Project phases
    Project deliverables
       List of deliverables by phases
       Descriptions of deliverables
    Resource assumptions
       Number of resources, skill levels, percentage assignment
    Deliverable estimates (effort, cost, duration)
    Estimate project duration
Size Estimate (Deliverables-based)

 Deliverables Sample list
 Approved vendor
 Data conversion plan
 Data definitions, data dictionary, etc
 Development strategy
 Disaster recovery plan
 Program specifications
 Regression test data
 Risk analysis
 Test plan, test data, etc
 Usability testing
 Training
Size Estimate (Functional Point)

Functional Point Estimate
   Used to size size system application from an end-
    user perspective.
      From business or logical point of view
      Independent of hardware, programming language,
       techniques, and tools used to developed the final system

      A functional point is defined as one end-user business
       function.
      The amount of functionalities in the project determines
       the project problems’ size.
Size Estimate (Functional Point)

FPA Problems
   Any functional point based estimate developed prior to the
    end of logical design are questionable
   FPA does not often consider non-business features of the
    systems e.g.
      Walk-throughs, inspections, team training, PM, etc
   Converting FP estimates into project duration and schedules
    can produce dubious results and lead to poorly defined plans
Size Estimate (COCOMO model)

COCOMO model
   Level of personnel
      PL = ƒ (∑EP,N, KSLOC)
   Level of complexity
      SEM = class of complexity * (KSLOC)
   Project size

   Reliability factor

   Development environment
          Task-based Estimate

Task-based estimates
   Task effort
      The number of work hours needed to complete a given
       task. It depends on task complexity and skill of the
       person assigned to the task


   Task Duration
      Elapsed time needed to complete a given task. Measured
       in days, weeks, or months.
          Task-based Estimate

Getting a reliable task-based estimate
   Ask the person to whom the task is assigned to estimate its
    duration
   The PM estimates the duration of various tasks, keeping in
    mind the team skill, knowledge, interruptions, and
    productivity environment
   The PM gathers a representative group of team members
    and they collectively estimate task effort and/or duration
   Use historical data from a similar project.

								
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