software project cost estimation
TRANSCRIPT
Software Project Cost Software Project Cost EstimationEstimation
UsingUsingFunction PointsFunction Points
By By Drew TkacDrew Tkac
Program Estimation ExampleProgram Estimation Example• Phone order company thinks they need a customer /
order taking program.• New customer contact information is entered into data
base controlled by the program. Fields are:– First Name– Last Name– Street Address– City– State– Zip Code– Phone Number– Initial Contact Date
Program Estimation ExampleProgram Estimation Example• Inventory data base, controlled by another program, is referenced
for orders.– Stock Number– Quantity in Stock– Selling Price
• Customer order data base is maintained by the program. Fields are:– First Name– Last Name– Stock Number of Item Purchased– Quantity Purchased– Date of Purchase
• All records within the program may be created, modified or deleted.• How long will it take and how much will it cost to write
this program?
The Point of Function Points….The Point of Function Points….
• A unit of software work• Generated during the requirements stage
for size and effort estimation.• Worst estimation technique, ahead of all
the others.• Something to count at the requirements
stage as opposed to lines of code.• Calibrated to type of software and past
staff performance.
Function Point Users GroupFunction Point Users Group• The standard for function point counting is
International Function Point Users Group (IFPUG) www.ifpug.org
• Offer classes, seminars and certification.• Maintain data bases and references.
Useful Regardless of Software Useful Regardless of Software ModelModel
Requirements Design Implementation Verification Maintenance
Adaptive Predictive
Big GiantRequirements
Bite SizedRequirements Design Implementation Verification Maintenance
Predictive
Adaptive
Function Points Useful to….Function Points Useful to….• The business / department
– Used to determine ROI– What features can be compromised?
• The technical staff / consultant– Used to determine staffing requirements– Used for performance review– Used to establish schedule– Used to estimate cost
Function Points ProvideFunction Points ProvideAn EstimateAn Estimate
• How long does it take you to get here from home?
• Normal conditions: 10 min.• Could it ever be 1 min?• Could it ever be 20 min?• Could it ever not happen?• Estimation – Has a probability attached – 98% of
the time it takes 10 min +/- 2 min
Software Cost Estimates:Software Cost Estimates:Black Art or Real Science?Black Art or Real Science?
• Currently typical software organizations are struggling to avoid estimates that are incorrect by 100% or more.
• Most common estimation technique - compare new project with past project based on personal memory. Guessing, intuition and unstructured expert judgment are used for 60% to 85% of estimates.
Results of Past ProjectsResults of Past Projects
Some Past Project SizesSome Past Project Sizes
Performing Function Point Performing Function Point AnalysisAnalysis
1. Start with the project requirements.2. Count function points. 3. Convert function points to lines of code based
on programming language.4. Convert lines of code to programmer hours
based on project type, and performance history.
5. Convert programmer hours to dollars using average values or staff salaries.
Characteristics of a SoftwareProgram
Input Output
External Files
Process
Internal Files
Program
What to Count?What to Count?
• External Inputs (EI)• External Outputs (EO)• External Queries (EQ)• Internal Logical File (ILF)• External Interface File (EIF)
External Inputs (EI)External Inputs (EI)• Screens, forms, dialog boxes, or control signals
through which an end user or other program adds, deletes, or changes program data.
• Grouped logically.• Number of data elements determine the logical
inputs complexity. (Data element type DET)• Include any input that has a unique format or
unique processing.
External Input ExampleExternal Input Example
NameStreet Address
Zip
Phone
Part Number
Part Description
Program
1 External Input with 4 DET
1 External Input with 2 DET
External Outputs (EO)External Outputs (EO)• Screens, reports, graphs, or control
signals that the program generates for use by an end user or other program.
• Grouped logically.• Number of data elements determine an
outputs complexity. (DET)• They include any output that has a
different format or different processing than other types.
External Output ExampleExternal Output Example
Program
1 External Output with 4 DET
First NameLast Name
Date of Purchase
Item Purchased
External Queries (EQ)External Queries (EQ)• Input/output combinations in which an
input results in an immediate, simple output.
• Receive data directly from a data base with little formatting.
Internal Logical Files (ILF)Internal Logical Files (ILF)• Major logical groups of end user data that
is completely controlled by the program.• Number of data elements control
complexity.• Single table in a data base or a data file
External Interface Files (EIF)External Interface Files (EIF)• Files controlled by another program with
which the program interacts.• Major logical group of data.• Number of data elements control
complexity.
Tally the Points, Accounting Tally the Points, Accounting WorkWork
• Each EI, EO, EQ, EIF, and ILF have values attached.
• Complexities for each are considered.• Additional factors are applied to produce
adjusted function points.• Can be cross checked to other methods.• Tables are available via IFPUG
The Dutch MethodThe Dutch Method• Works well early in the project• High degree of uncertainty• Best applied to data base related projects• Great to determine if the project is worth
taking the next step.• Developed by Netherlands Software
Metrics Association (NESMA)• Formula: Function Point Count = (35 X Internal
Logical Files) + (15 X External Interface Files)
Convert Function Points to Lines Convert Function Points to Lines of Codeof Code
Lines of Code per Staff MonthLines of Code per Staff Month
Diseconomies of ScaleDiseconomies of Scale
Convert Staff Hours to CostConvert Staff Hours to CostProgrammer’s SalariesProgrammer’s Salaries
Haskell $198,000
Erlang $99,000
Objective-C $82,000
Pascal $81,000
C++ $80,000
SmallTalk $80,000
TCL $80,000
C# $79,000
Java $79,000
Python $78,000
Perl $77,000
Ruby $74,000
COBOL $73,000
JavaScript $72,000
ColdFusion $64,000
Delphi $64,000
PHP $64,000
Visual Basic $64,000
C $60,000
Our ExampleOur ExampleCalculate Function PointsCalculate Function Points
• Internal Logical Files– Customer Contact File– Customer Purchase File
• External Interface Files- Inventory Data Base
• Using the Dutch Method:FP = (35 X 2) + (15 X 1) = 85 FP’s
Our ExampleOur ExampleConvert Function Points to Lines of CodeConvert Function Points to Lines of Code
• Choose the programming language that requires the fewest number of lines of code to implement a function point
• Consider cost of a programmer for this language and availability
• Consider maintenance factors• My choice was: Visual Basic • Example program: 32 lines of code / function
point or 32 X 85 = 2720 LOC
Our ExampleOur ExampleConvert Lines of Code to CostConvert Lines of Code to Cost
• VB Programmers $64K / year X 1.25 benefits = $80K / 12 months = $6667/mo
• Lines of code per month for a business system, medium performance, small project = 3000
• 2720 Lines of code / 3000 Lines of code per month = 0.9 Months or $6045
ReferencesReferencesGarmus, David and Herron, David, Function Point Analysis,
ISBN-0-201-69944-3
McConnell, Steve, Software Estimation, ISBN10: 0-7356-0535-1
International Function Point Users Group
Brooks, Fred, The Mythical Man-Month: Essays on Software Engineering