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Software Project Planning

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throughout the software lifecycle, there are many decision situations involving ... unless a software project has clear definitions of its key milestones and ... – PowerPoint PPT presentation

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Title: Software Project Planning


1
Software Project Planning
  • Infsy 570
  • Dr. R. Ocker

2
SWE economics analysis (Boehm, 84)
  • throughout the software lifecycle, there are many
    decision situations involving limited resources

3
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?

4
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

5
Question must ask
  • How much information-buying is enough?

6
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

7
project estimation
  • first step in project planning
  • estimate resources, cost, and schedule for sw
    development project
  • requires experience and access to historical
    information

8
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

9
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

10
Activities associated with project planning
  • Software scope
  • resources
  • project estimation
  • decomposition

11
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

12
2. resources
  • must estimate resources required to accomplish
    the development effort
  • fig. 5.2 development resources pyramid

13
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

14
b. reusable sw components
  • next level, can reduce development costs
  • reuse considerations often ignored
  • can greatly reduce development time

15
c. people - top of pyramid
  • select skills needed

16
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

17
3. project estimation
  • cost estimates must be provided up front
  • but... the longer we wait, the more we know, and
    the better our estimates

18
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

19
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

20
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

21
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)

22
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)

23
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)

24
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

25
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

26
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

27
5. empirical estimation models
  • The COCOMO Model Constructive Cost Model Boehm,
    1984
  • hierarchy of 3 increasingly detailed software
    estimation models

28
model 1
  • Basic COCOMO model
  • computes effort and cost estimated as LOC

29
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

30
model 3
  • Advanced COCOMO model
  • incorporates the intermediate version with an
    assessment of the cost dirvers impact on each
    step (analysis, design, etc.)

31
Steps for intermediate level (see Boehm, 1984 for
detailed example)
  • Four steps

32
Step 1 - Nominal effort estimation
  • determine projects development mode (organic,
    semidetached, embedded)
  • estimate size of the project

33
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

34
Step 3 - Estimate development effort
  • compute estimated development effort nominal
    effort X product of effort multipliers for 15
    cost driver attributes

35
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

36
9 Management Guidelines for better cost
estimating (Lederer and Prasad)
  • paper reports results of survey on cost
    estimating practices of 115 computer
    professionals

37
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

38
Guidelines
  • Based on results of survey, authors developed 9
    guidelines for better cost estimation

39
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

40
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!

41
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!

42
4. Monitor the progress of the proposed project
43
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

44
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

45
7.Computing management should carefully study and
approve the cost estimate
  • need to conduct a cost/benefit review before
    system development begins

46
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

47
9. Dont rely on cost estimating software for an
accurate estimate.
  • packages dont improve estimation, and lower the
    satisfaction level of the estimators

48
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

49
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

50
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
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