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Shashwat [email protected]
Estimating the cost of a Software product is one of the most
difficult and error prone tasks. Cost estimates can be of two
types: 1) Top down approach
2) Bottom up approach
TOP DOWN APPROACH
♣ It focuses on system level cost like computing resources as well as the
cost of configuration management ,quality
assurance ,system integration ,training and
publications.♣ It focuses on system level cost but
may overlook various technical factors.
BOTTOM UP APPROACH
♣ It first estimates the cost to develop each module and these
cost are combined to arrive at an overall estimate.
♣ It emphasizes the cost associated with developing individual system components but fail to account for
system level costs.
METHODS FOR ESTIMATION
1) Expert Judgment
2) Delphi Cost Estimation 3) Work Breakdown Structures
4) Algorithmic Cost Models
Compute the estimate cost of the software system as the sum of costs of the modules and the subsystem that comprises the
system. They follow Bottom Up Approach.
CONSTRUCTIVE COST MODEL
☺ This is one of the most widely used and discussed software cost
estimation in the industry.☺ It has evolved into a more
comprehensive estimation model called COCOMO II.
☺In the COCOMO model Effort Multipliers are used to adjust the
estimate for product attribute ,computer
attribute ,personal attribute and project attribute.
☺ The following activities are covered by the estimates:
a) Covers estimate through acceptance testing
b) Includes the cost of documentation and reviews.
c) Includes the cost of Project Manager.
☺ The cost estimators exclude planning and
analysis costs ,installation and training cost and cost of computer
operators , secretaries.☺ The DSI (Delivered Source
Instruction) estimate includes job control statement and source
statements but excludes comments
☺ It is considered to be one line or card image.
Following are the assumptions estimated by the COCOMO concerning the nature of the software:-
1) Careful definition and validation of requirements is performed by a small number of capable people. 2) Requirements remain stable
throughout the project 3) Careful definition and validation
of architectural designs is performed by a small number of
capable people.
4) Detailed design ,coding and unit testing are performed in parallel by group of programmers working in
teams. 5) Integration Testing is based on
early test planning.6) Interface errors are found by unit
testing and by inspections.
Formally there are mainly 10 steps to estimate the cost
using COCOMO:-
1) Identify all the subsystem and modules in the product.
2) Estimate the size of each module and calculate the size of
each subsystem and the total system.
3) Specify the module level multipliers.
4) Compute the module effort and the time estimates for each
modules. 5) Specify the effort multipliers
for each subsystems. 6) From Steps 4 and 5 compute
the estimated effort and development time for each
subsystems.
7) From Step 6 compute the total system effort and
development time. 8) Perform sensitivity analysis
on the estimate. 9) Add other development cost
like planning and analysis that are not included in the estimates.
10) Compare this estimate with the one developed by Delphi
estimation .Identify and Rectify the differences in the estimates.
MODULE LEVEL MULTIPLIERS
Product Complexity Programmers Capability
Virtual Machine ExperienceProgramming Language Experience
EFFORT MULTIPLIERSPERSONAL ATTRIBUTES
• Analyst capability•Programmer capability•Application experience
• Virtual machine experience• Programming language
experience PROJECT ATTRIBUTES
• Use of modern programming practices
• Use of software tools• Required schedule
PRODUCT ATTRIBUTES Required Reliability
Data-base Size Product Complexity
COMPUTER ATTRIBUTES Execution time constraint Main storage Constraint Virtual machine reality
Computer turnaround time
ADVANTAGES:-
o The model can be used to gain insight into the cost factors.
o Systematic techniques of software engineering are used throughout
the development process.o Data can be collected and analyzed ,new factors can be
identified and effort multipliers can be adjusted.
Shashwat [email protected]
