Lect 4 Cost Estimation
Transcript of Lect 4 Cost Estimation
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7/31/2019 Lect 4 Cost Estimation
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Software Cost Estimation
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Software cost estimation
q Predicting the resources required
for a software development process
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Fundamental estimation questions
q How much effort is required to complete an
activity?
q How much calendar time is needed to complete
an activity?q What is the total cost of an activity?
q Project estimation and scheduling and
interleaved management activities
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Software cost components
q Hardware and software costs
q Travel and training costs
q Effort costs (the dominant factor in most
projects) salaries of engineers involved in the project
Social and insurance costs
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Effort costs must take overheads into account costs of building, heating, lighting costs of networking and communications
costs of shared facilities (e.g library, staff restaurant, etc.)
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Costing and pricing
q Estimates are made to discover the cost, to the
developer, of producing a software system
q There is not a simple relationship between the
development cost and the price charged to thecustomer
q Broader organisational, economic, political and
business considerations influence the pricecharged
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Software pricing factors
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q Size related measures based on some output
from the software process. This may be lines of
delivered source code, object code instructions,
etc.q Function-related measures based on an estimate
of the functionality of the delivered software.
Function-points are the best known of this type of
measure
Productivity measures
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q Estimating the size of the measure
q Estimating the total number of programmer
months which have elapsed
q Estimating contractor productivity (e.g.
documentation team) and incorporating this
estimate in overall estimate
Measurement problems
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q Real-time embedded systems, 40-160
LOC/P-month
q Systems programs , 150-400 LOC/P-month
q Commercial applications, 200-800
LOC/P-month
q In object points, productivity has been measured
between 4 and 50 object points/monthdepending on tool support and developer
capability
Productivity estimates
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Factors affecting productivity
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Estimation techniques
q Algorithmic cost modelling
q Expert judgement
q Estimation by analogy
q Parkinson's Law
q Pricing to win
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Algorithmic code modelling
q A formulaic approach based on historical cost
information and which is generally based on the
size of the software
q Discussed later
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Expert judgement
q One or more experts in both software
development and the application domain use
their experience to predict software costs.
Process iterates until some consensus isreached.
q Advantages: Relatively cheap estimation
method. Can be accurate if experts have direct
experience of similar systems
q Disadvantages: Very inaccurate if there are no
experts!
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Estimation by analogy
q The cost of a project is computed by comparing
the project to a similar project in the same
application domain
q Advantages: Accurate if project data availableq Disadvantages: Impossible if no comparable
project has been tackled. Needs systematically
maintained cost database
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Parkinson's Law
q The project costs whatever resources areavailable
q Advantages: No overspendq Disadvantages: System is usually unfinished
q PL states that work expands to fill the time available. Thecost is determined by available resources rather than by
objective statement.q Example: Project should be delivered in 12 months and 5
people are available. Effort = 60 p/m
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Pricing to win
q The project costs whatever the customer has to
spend on it
q Advantages: You get the contract
q Disadvantages: The probability that the
customer gets the system he or she wants is
small. Costs do not accurately reflect the work
required