Project Planning Control

							Project Planning & Tracking



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    Software Cost Estimation

• Most planning efforts begin with an
  estimate of the cost, in terms of
  time, money, or effort, of a project
• Cost estimation is very difficult in
  software development because it
  depends on so many factors


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   Cost Factor: Programmer Ability
A famous 1968 study by Harold Sackman
revealed the following differences between
programmers:
      Measure              Best : Worst
    Debugging time            28:1
    CPU development time      8:1
    Coding time               16:1
    Program size              6:1
    Running time              5:1

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  Cost Factor: Product Complexity
Program effort increases by a factor of
about 1.5 between each of the following
categories:
   – business application programs (payroll)
   – scientific application programs (stress analysis)
   – software tools (compiler)
   – system software (operating system)
   – embedded systems (avionics)

There is a total increase in effort of a factor
of about 7.5 across this spectrum
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      Cost Factor: Program Size
Large programs are much more difficult
to develop than small ones. Effort
seems to be an exponential function of
program size:

                               f
           effort = k * size

where f is a factor usually estimated
between 1.05 and 1.83
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    Cost Factor: Level of Reliability
• Reliability is the probability that a program
  will perform correctly under stated
  conditions for a given period of time
• Reliability can be low for programs whose
  failure only causes inconvenience, or very
  high when human life is at stake
• Effort varies by a factor of about 2 for
  programs at opposite ends of this
  spectrum
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          Cost Factor:
    Development Environment
• Productivity increases by a factor of
  between 5 and 10 when a high level
  language is used instead of
  assembler
• Effort decreases by about half when
  developers work in an excellent
  development environment

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    Cost Factors: Summary

Taken together, these (and other)
cost factors make it clear that effort
for developing a program can vary
over several orders of magnitude,
thus making software project cost
estimation very hard.


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      Cost Estimation: Analogy
An expert estimates the cost of the
current project by comparing it with
past, similar projects.
 – cheap, easy, and often accurate technique
 – fails when there is no experience with
   similar projects in the past
 – fails when estimators overlook important
   cost factors

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    Cost Estimation: Delphi Method
Developed at the Rand Corporation in 1948 for
achieving expert consensus without group
conflict:
 – a team of experts is formed and asked not to discuss
   their work with one another
 – a coordinator provides each expert with project
   information and asks for an estimate
 – coordinator distributes anonymous estimates, with
   comments, and asks for revised estimates
 – process continues until consensus is reached
Usually works well, but is expensive and time
consuming.
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 Cost Estimation: Bottom-Up Technique
• Breaks a project into parts, estimates
  the cost of the parts, then combines
  all estimates to achieve an overall
  estimate
• Projects may be broken down by:
  – sub-systems or modules
  – life cycle phases
  – project tasks
  – work assignments
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 Work Breakdown Structure

A work breakdown structure (WBS)
is a tree whose root represents an
   entire project or product, and
  whose other nodes represent a
 hierarchical decomposition of the
         project or product.


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      Bottom-Up Techniques
  Advantages and Disadvantages
+ Make all project or product parts
  explicit, thus providing a basis for
  scheduling and resource assignments
+ Easy and cheap method to apply
– Low level estimates are usually made
  by analogy, and so may fail for new
  products or tasks


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Cost Estimation: Algorithmic Cost Models
• Provide computational means for deriving
  estimates as functions of important cost
  factors
• Functions used contain constants derived
  from statistical analysis of data from past
  projects:
  – can only be used if data from past projects is
    available
  – must be calibrated by knowledgeable analysts
  – relies on initial size and cost factor estimates which
    themselves are questionable
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Scheduling & Resource Assignment
     Scheduling is planning when a
           task will occur.

        Resource assignment is
    planning which people and other
        assets to use for a task.

     Control, tracking, or monitoring
    is comparing plans to reality and
        adjusting plans as needed.

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Scheduling & Resource Assignment Tools
 Two graphical tools are widely used
 for these scheduling and resource
 assignment:
    – Gantt Charts
    – PERT/CPM Charts

 Gantt and PERT charts are
 sometimes combined to incorporate
 the advantages of both.

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     Gantt Chart

 A Gantt chart is a bar
chart that plots tasks or
resources against time.




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        Gantt Example—Resources
               Week 1   Week 2   Week 3   Week 4

Front-Loader


Dump-Truck 1


Dump-Truck 2


Supervisor


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            Gantt Chart
    Advantages and Disadvantages
+ Gantt charts are simple and can show
  many aspects of tasks and resources
  clearly
– Gantt charts do not lend themselves to
  computation of schedule attributes like
  completion dates, slack time, etc.
– Gantt charts are difficult to use for project
  tracking without computer support
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     PERT/CPM Chart

A PERT/CPM chart is a directed
 graph that shows tasks, their
      durations, and their
precedence relationships, and
  allows estimation of project
       completion times.



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           PERT Example
                    Task 2
                    6 units


Task 1                                  Task 5
4 units                                 3 units

          Task 3              Task 4
          2 units             3 units



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           PERT Chart
   Advantages and Disadvantages
+ PERT charts support sophisticated
  techniques for analyzing schedules
– PERT charts do not show task durations
  graphically and may be difficult to read
– PERT charts are difficult to analyze
  without computer support
– PERT charts are difficult to use for project
  tracking without computer support
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Hybrid Gantt/PERT Charts


  Hybrid charts that show task
durations like Gantt charts, and
 task precedence relationships
 like PERT charts, can provide
  the advantages of both tools.




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    Project Management Software
Improved Planning—all tasks and their
  relationships must be considered and
  documented in detail
Improved Cost & Time Estimation—the software
  computes them correctly and consistently
Improved Communication—detailed, up-to-date
  reports are easily generated
Improved Tracking—actual completion dates
  and resource costs are easy to add and
  incorporate into schedules and estimates
Overall Improvement—many inconsistencies are
  detected by the software
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  Project Planning & Estimating Tools
Activity   Percent of Projects With Automation

 Sizing                        15
 Cost estimating               25
 Quality estimating             3
 Planning                      65
 Tracking                      35
 Measuring productivity         5
 Measuring quality             15
 Assessing                     10

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        Advantages of Tool Use
For large projects (more than 250 KLOC):
– Manual planning and estimating:
   » 40% at least 6 months late
   » 15% at least 12 months late
– Automated planning or estimating, but not both:
   » 12% at least 6 months late
   » 5% at least 12 months late
– Both automated planning and estimating:
   » 5% at least 6 months late
   » 1% at least 12 months late
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