Software Project Planning

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Software Project Planning

• Infsy 570
• Dr. R. Ocker

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SWE economics analysis (Boehm, 84)

• throughout the software lifecycle, there are many
  decision situations involving limited resources

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Examples

• feasibility phase
• how much should we invest in analyses?
• plans and requirements phase
• how rigorously should we specify requirements?
• design phase
• should we use existing sw which does not
  completely meet the requriements?
• test phase
• how much testing is enough?

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Analyzing risk and uncertainty

• can apply basic micro economic analysis to these
  questions
• in sw engineering, must make decisions under
  conditions of uncertainty
• can reduce uncertainty, and therefore make better
  decisions, by buying information
• e.g. prototyping is a way of buying information
  to reduce uncertainty about risky functionality

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Question must ask

• How much information-buying is enough?

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Project Planning

• sw project management process begins with project
  planning
• objective of sw project planning - to provide a
  framework for manager to make reasonable
  estimates of resources, costs and schedules

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project estimation

• first step in project planning
• estimate resources, cost, and schedule for sw
  development project
• requires experience and access to historical
  information

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project estimation

• estimation is risky business - lots of
  uncertainty due to
• project complexity
• project size
• degree of structural uncertainty - degree to
  which requirements are solidified
• availability of historical information
• risk - measured by degree of uncertainty in
  quantitative estimates

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project estimation

• evolutionary process models - iterative view of
  development
• possible to revise the estimate
• estimates made at beginning of sw project
• should be updated regularly
• estimates should define best case and worst
  case

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Activities associated with project planning

• Software scope
• resources
• project estimation
• decomposition

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1. software scope

• want to establish a project scope that is
  unambiguous and understandable at management and
  technical levels
• describes
• function
• performance
• constraints
• interfaces
• reliability

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2. resources

• must estimate resources required to accomplish
  the development effort
• fig. 5.2 development resources pyramid

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a. hw and sw tools

• foundation of resources pyramid, provides
  infrastructure to support development
• sw engineering environment
• must prescribe the time-frame required for hw and
  sw
• verify that these resources will be available

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b. reusable sw components

• next level, can reduce development costs
• reuse considerations often ignored
• can greatly reduce development time

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c. people - top of pyramid

• select skills needed

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each resource specified with 4 characteristics

• 1. description of resource
• 2. statement of availability
• 3. chronological time resource will be needed
• 4. duration of time resource used

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3. project estimation

• cost estimates must be provided up front
• but... the longer we wait, the more we know, and
  the better our estimates

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a. use of decomposition techniques

• divide and conquer approach
• decompose project into major functions and
  related swe activities
• cost and effort estimates performed in stepwise
  fashion

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b. empirical estimation models

• can complement decomposition techniques or used
  alone
• model is based on historical data
• examples LOC, FP
• SW cost estimation relies on good historical data

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4. decomposition techniques

• decompose the problem (i.e., sw project
  estimation) into set of smaller problems
• from chp. 3 - 2 types of decomposition
• a. decomposition of the problem
• b. decomposition of the process
• before decomposition, must understand project
  scope and generate estimate of project size
• accuracy of estimate strongly influenced by
  accuracy of size estimate

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Problem-based estimation

• direct measure - LOC
• indirect measure - FP
• a. begin with bounded statement of sw scope
• b. decompose sw into problem functions that can
  each individually be estimated
• c. apply sizing measure to each function
• e.g. LOC, FP, OO (classes, objects)
• d. apply baseline productivity metrics (e.g.,
  LOC/pm, FP/pm)

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decomposition

• decomposition is different for LOC vs. FP
• for LOC - decomposition must be detailed
• for FP - looking at input, output, inquiries,
  data files, interfaces etc.
• planner uses historical data or intuition (not
  recommended)

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estimation

• make 3 estimates for each function
• optimistic, most likely, pessimistic
• then compute 3 point or expected value
• see 5.1
• then apply historical LOC or FP productivity data
  (e.g. FP/pm)

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Process-based estimation

• most common technique for estimating project
• process is decomposed into a small set of
  activities or task
• effort required to complete each is estimated

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Process-based estimation

• a. determine sw functions using project scope
  document
• b. meld sw process activities and functions
• determine sw process activities that must be
  performed for each function
• functions and process activities can be part of
  a table - see fig 3.2

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Process-based estimation

• c. apply average labor rates to the effort
  estimated for each process activity
• d. compute costs and effort for each function
  and software process activitey
• can perform process-based estimate independently
  of LOC or FP
• then have 2-3 estimates of cost and effort to
  compare and reconcile

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5. empirical estimation models

• The COCOMO Model Constructive Cost Model Boehm,
  1984
• hierarchy of 3 increasingly detailed software
  estimation models

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model 1

• Basic COCOMO model
• computes effort and cost estimated as LOC

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model 2

• Intermediate COCOMO model
• computes effort and cost using a set of cost
  drivers
• includes subjective assessments of product, hw,
  personnoel, and project attributes

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model 3

• Advanced COCOMO model
• incorporates the intermediate version with an
  assessment of the cost dirvers impact on each
  step (analysis, design, etc.)

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Steps for intermediate level (see Boehm, 1984 for
detailed example)

• Four steps

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Step 1 - Nominal effort estimation

• determine projects development mode (organic,
  semidetached, embedded)
• estimate size of the project

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Step 2 - Determine effort multipliers

• 15 cost drivers within model - each has a rating
  scale and a set of effort multipliers which
  modifies step 1 estimate

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Step 3 - Estimate development effort

• compute estimated development effort nominal
  effort X product of effort multipliers for 15
  cost driver attributes

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Step 4 - Estimate related project factors

• model has additional costing estimation
  relationships for computing dollar cost of
  project and for breakdown by lifecycle phase and
  by type of project acitivity
• can estimate project schedule

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9 Management Guidelines for better cost
estimating (Lederer and Prasad)

• paper reports results of survey on cost
  estimating practices of 115 computer
  professionals

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Need for better estimates

• 63 of all large projects (over 50,000)
  significantly overrun cost estimates
• only 25 of projects completed at cost reasonably
  close to project estimate

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Guidelines

• Based on results of survey, authors developed 9
  guidelines for better cost estimation

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1. Assign the initial estimating task to the
final developers

• 2 approaches
• a. separate-function approach
• use experienced group of estimators to conduct
  the feasibility study and prepare initial project
  estimate
• b. combined-function approach
• final analysts and programmers prepare initial
  estimate during feasibility study
• get more accurate estimates with this approach

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2. Delay finalizing the initial estimate until
the end of a thorough study

• often prepare initial cost estimate at beginning
  of project and then revise it (repeatedly) during
  the project
• found that revision of estimate does not increase
  accuracy
• people seem to look to the original estimate, not
  the revised estimate, when judging cost
  estimation accuracy -- so better to be right the
  first time!

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3. Anticipate and control user changes

• when lots of changes, like trying to estimate
  cost of a moving target
• estimators need to thoroughly understand user
  requirments before they estimate its cost
• should be able to reduce and control frequent
  change requests
• discourage unnecessary user changes - charge
  extra!

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4. Monitor the progress of the proposed project
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5. Evaluate project progress by using independent
auditors

• most projects usually monitored by those involved
  in it
• more accurate estimates occur when independent
  auditors are present

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6. Use the estimate to evaluate project personnel

• cost estimating used more for project planning
  and control than for evaluation of personnel
• could use positive rewards for personnel who
  provide accurate estimates and for those that
  meet the estimates

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7.Computing management should carefully study and
approve the cost estimate

• need to conduct a cost/benefit review before
  system development begins

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8. Rely on documented facts, standards, and
simple arithmetic formulas rather than guessing,
intuition, personal memory, and complex formulas.

• greater accuracy found when do the above
• less accuracy when rely on intuition and personal
  memory, which is customary

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9. Dont rely on cost estimating software for an
accurate estimate.

• packages dont improve estimation, and lower the
  satisfaction level of the estimators

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Words of wisdom

• there is no way a cost estimation technique can
  compensate for the lack of definition or
  understanding of the sw job to be done

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Words of wisdom

• there is no magic formula that will provide an
  easy and accurate substitute for the process of
  thinking through and fully understanding the
  nature of the software product to be developed

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Words of wisdom

• unless a software project has clear definitions
  of its key milestones and realistic estimates of
  the time and money it will take to achieve them,
  there is no way that a project manager can tell
  whether the project is under control or not