Function Points I EEE493 2000

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Function Points I EEE493 2000
Royal Military College of Canada Electrical and
Computer Engineering

• Major Greg Phillips
• greg.phillips_at_rmc.ca
• 1-613-541-6000 ext. 6190

Dr. Scott Knight knight-s_at_rmc.ca 1-613-541-6000
ext. 6190
2
Refs

• Pressman, R.S., Software Engineering a
  Practitioners Approach 5th Ed., McGraw-Hill,
  2001, Chapter 4
• Capers Jones, What are Function Points,
  www.spr.com/library/0funcmet.htm
• Boehm, Ray, Function Point FAQ, Software
  Composition Technologies, Inc., 1997,
  http//ourworld.compuserve.com/homepages/softcomp/
  fpfaq.htm
• Dreger, J.D., Function Point Analysis,
  Prentice-Hall, 1989

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Teaching Points

• The software productivity paradox
• Measuring by counting business functions
• Identifying different business function types

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Review

• What is the philosophy behind Wideband Delphi?
• What is a good unit of measure?

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What is a Good Unit of Measure?

• Consider lines of deliverable source code - LOC
• ProductivityGoods or services produced per
  unit of labour and expense
• Does moving to a higher-order language compiler
  increase productivity?

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A Measure of Productivity

• "Goods or services produced per unit of labor and
  expense."

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Consider This Estimate
ACTIVITY CASE A
CASE B
ASSEMBLER FORTRAN
VERSION
VERSION
(10,000 LINES) (3,000 LINES) DIFFERENCE

-------------- -------------- --------------
Requirements 2
Months 2 Months 0
Design 3 Months
3 Months 0
Coding 10 Months 3
Months - 7
Integration/Test 5 Months 3
Months - 2 User
Documentation 2 Months 2 Months
0
Management/Support 3 Months 2
Months - 1
-------------- --------------
-------------- Total
25 Months 15 Months -
10
-------------- -------------- --------------
Total Costs
125,000 75,000 - 50,000
Cost Per Source Line 12.50
25.00 12.50
Lines Per Person Month 400
200 - 200
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The Software Productivity Paradox

• Software involves a substantial number of
  activities that behave like fixed or inelastic
  costs that are not associated with coding.
• Requirements analysis
• writing specifications (analysis/design)
• generating user documentation
• project planning/management
• configuration management/change control
• Increasing the efficiency of code generation
  increases the cost per line of source code!

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A different Measure of Productivity

• In the late 1970's A.J. Albrecht of IBM took the
  position that the economic output unit of
  software projects should be valid for all
  languages, and should represent topics of concern
  to the users of the software.
• Measure the functionality of software
• the external aspects of software visible to the
  user
• the users functional requirement

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Business Functions

• The external aspects/ units of functionality
  visible to the user are
• the inputs to the application
• the outputs from the application
• inquiries by users
• the data files that would be updated by the
  application
• the interfaces to other applications

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Weighting the Business Functions

• empirical weighting factors were developed for
  the five business function types
• e.g. if we had identified one function of each
  type

FUNCTION RAW DATA
WEIGHTS POINTS
1 INPUT X 4 4
1 OUTPUT X 5
5 1 INQUIRY X 4
4 1 DATA FILE
X 10 10 1
INTERFACE X 7 7
----
UNADJUSTED TOTAL
30 COMPLEXITY
ADJUSTMENT NONE
ADJUSTED FUNCTION POINTS 30
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Now Consider This Estimate
ACTIVITY CASE A
CASE B
ASSEMBLER FORTRAN
VERSION
VERSION
(30 F.P.) (30 F.P.) DIFFERENCE

-------------- -------------- --------------
Requirements 2
Months 2 Months 0
Design 3 Months
3 Months 0
Coding 10 Months 3
Months - 7
Integration/Test 5 Months 3
Months - 2 User
Documentation 2 Months 2 Months
0
Management/Support 3 Months 2
Months - 1
-------------- --------------
-------------- Total
25 Months 15 Months -
10
-------------- -------------- --------------
Total Costs
125,000 75,000 - 50,000
Cost Per F.P. 4,166.67
2,500.00 - 1,666.67
F.P. Per Person Month 1.2
2.0 0.8
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Finding Business Functions

• We count only those business functions that are
  approved
• benefits to the end user
• Not
• job control/ operating system functions
• not temporary files
• nothing implementation specific

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Disclaimer

• Real function point counting systems are complex
• They require carefully defined function point
  counting guides and practices
• We will use a small example system to illustrate
  the ideas underlying function point counting
• The small example system used is not defined
  precisely enough to be used to count real systems
• For a real FP counting system see
• The International Function Points Users Group

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Finding Business Functions
End User
Transactions
Input
Output
Inquiry
Application A
Application B
Interface
Shared Interface
A Files
B Files
Interface
Output
Input
Transactions
Transactions
Inquiry
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The 5 Function Types

• Inputs - ITs
• Outputs - OTs
• Inqueries - QTs
• Files - FTs
• Interfaces - ETs

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How We Count

• Count business functions
• Identify business functions
• classify the identified functions
• Adjust raw FP total
• based on application characteristics

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Identifying Outputs

• Each unique user data or control output
• I.e. things that leave the context boundary
• Unique means
• it has a different format
• it has the same format but requires different
  processing
• Example a report that needs to be generated on a
  daily, weekly and monthly bases in both a GUI
  screen version and a printed version has 6
  different outputs
• Example Presenting a table of data on a screen
  and a summary of the table at the bottom of the
  screen are 2 different outputs

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Finding Business Functions
End User
Transactions
Input
Output
Inquiry
Application A
Application B
Interface
Shared Interface
A Files
B Files
Interface
Output
Input
Transactions
Transactions
Inquiry
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Identifying Inputs

• Each unique user data or control input
• I.e. things that enter the context boundary
• Unique means
• it has a different format
• it has the same format but requires different
  processing
• Example to screens appear identical but cause a
  internal entities to be modified in different
  ways or cause the update of different logical
  internal files

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Identifying Inquiries

• Each unique user data or control input/output
  combination in which on-line user-defined input
  causes and generates an immediate on-line output
• Unique means
• it has a different format in either the input or
  output portion
• it has different processing logic in either the
  input or output portion

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Identifying Inquiries (contd)

• Must have a simple keythe output must be a
  single record or group of related records - I.e.
  not a range of records
• The output response must be immediate
• The inquiry must not update/change any records

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Identifying Logical Files

• Each major logical group of user data or control
  information maintained entirely within the
  application boundary
• Unique means
• master files that are lasting or permanent data
  needed to recorded by the application
• a logical collection of data as seen by the user
• NOT - files/groups of temporary transactions or
  lists of events that may be used to update
  another file

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Identifying Interfaces

• Each major logical file or other group of data or
  control information within the application the
  application boundary that is sent to, shared
  with, or received from another application
• This can include transaction files
• Files shared between applications are counted
  both as FTs and ETs

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Identifying Interfaces (contd)
Consider Appln A
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When can we Count?

• In early product planning?
• During requirement specification?
• After requirement specification?
• After Design?
• After Delivery?

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Next ClassFunction Points II