Webinar: Function Point Primer June 2008 Sheila P. Dennis, CFPS - - PowerPoint PPT Presentation

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Webinar: Function Point Primer June 2008

Sheila P. Dennis, CFPS Vice President, Software Sizing Services David Consulting Group sdennis@davidconsultinggroup.com

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• DCG is an international IT process improvement and measurement company

currently managing active engagements with over 20 Fortune 1,000 companies and government agencies around the world.

• DCG’s focus is directed toward practical implementations that measure results,

improve IT processes and deliver value.

• DCG is a recognized world leader in Software Sizing. It’s founders “wrote the

book” on Function Point Analysis.

• DCG consistently promises and delivers positive change in its consulting

engagements.

• DCG makes all of this possible through the expertise and commitment of its

consultants who are organized into the following Consulting Practices:

• Software Process Improvement ­ including CMMI and Six Sigma
• Software Sizing ­ using IFPUG Function point Counting and other

techniques

• Software Measurement ­ including estimating, benchmarks and
• utsourcing SLA definition, measurement and monitoring
• IT Performance Improvement ­ focused on IT Operations through ITIL

and IT Governance

• IT Decisions Coaching – helping individuals and teams in IT to

increase value by making better decisions.

About David Consulting Group

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Agenda

Function Point Analysis, Uses and Benefits

• Objectives of Function Point Analysis
• Benefits of Function Point Analysis
• Function Point Counting Process

Function Point Counting Rules

• Types of Function Point Counts
• Steps in Counting
• Data Functions
• Transactional Functions
• General System Characteristics

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Function Point Analysis is a standardized method for measuring the functionality delivered to an end user.

• Consistent method
• Easy to learn
• Available early in the lifecycle
• Acceptable level of accuracy
• Meaningful internally and externally
• Objectives
• Measure functionality that the user requests and receives
• Measure software development and maintenance

independently of technology used for implementation

Why Function Point Analysis?

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• A vehicle to estimate cost and resources required for

software development, enhancement and maintenance

• A tool to quantify performance levels and to monitor

progress made from software process improvement initiatives

• A tool to determine the benefit of an application to an
• rganization by counting functions that specifically match

requirements

• A tool to size or evaluate purchased application packages

Benefits of Using Function Points

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• Data Functions
• Internal Groupings of data called Internal Logical Files (ILF)
• External Groupings of data or External Interface Files (EIF)
• The term file does not refer to files in the physical sense,

rather refers to logical data stores, entities, objects or super­ classes

• Transaction Functions
• External Inputs (EI)
• External Outputs (EO)
• External Inquires (EQ)
• General System Characteristics
• We will explore the definitions of each of these

components as we go forward.

Overview

FP Evaluates These Components

External Input External Inquiry External Output Internal Logical Files External Interface File

Application

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Function Point Process

1. Determine the type of Function Point count 2. Identify the counting scope and application boundary 3. Count the data functions to determine their contribution to the unadjusted function point count (Determine the complexity and weight) 4. Count the transactional functions to determine their contribution to the unadjusted function point count (Determine the complexity and weight) 5. Determine the value adjustment factor ­ 14 General System Characteristics 6. Calculate adjusted function point count using the appropriate formulas

Process

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Types of Function Point Count

• Development Project Function Point Count
• Measures the functions provided to users with first install of

the software delivered when project is complete

• Enhancement Project Function Point Count
• Measures the modifications to existing application

add, change or delete user functions delivered when project is complete

• When functionality is installed, the application count must

be updated to reflect changes in the application functionality Step 1: Type of Count

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Types of Function Point Count

• Application Function Point Count
• Measures an installed application
• Also referred to as the baseline or installed count
• Provides count of the current functions provided to users
• Number is initialized when the development project function

point count is completed

• It is updated every time completion of an enhancement project

alters the application's functions Step 1: Type of Count

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Scope and Boundary

• Definition:
• A function point count provides an answer to a business

problem

• Purpose:
• Determines the type of function point count and scope of

required count

• Influences the positioning of the boundary between the

software under review and the surrounding software Step 2: Boundary

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Other Applications Application Boundary

External Input External Inquiry External Output

Other Applications

External Input External Output Internal Logical File External Interface File Internal Logical File

Diagramming an Application Boundary

Step 2: Boundary

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• Data functions represent the functionality provided

to the user to meet internal and external data requirements

• Internal Logical Files (ILFs)
• External Interface Files (EIFs)
• The term file here does not mean file in the

traditional data processing sense; in this case, file refers to a logically related group of data and not the physical implementation of those groups of data

Step 3: Data

Data Functions

Step 3: Data

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• An internal logical file (ILF) is a user identifiable

group of logically related data or control information maintained within the boundary of the application

• The primary intent of an ILF is to hold data

maintained through one or more elementary processes of the application being counted Step 3: Data

Internal Logical Files

Step 3: Data

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• To identify ILFs, look for groups of data or

control information that satisfy the definition

• f an ILF
• All of the following counting rules must

apply for the information to be counted as an ILF:

• The group of data or control information is logical and user

identifiable

• The group of data is maintained through an elementary

process within the application being counted

Step 3: Data

ILF Identification Rules

Step 3: Data

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ILF Examples

• Count as Internal Logical Files
• Application transaction data maintained within the application
• ILFs maintained by more than one application (Shared data)

Step 3: Data

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• An external interface file (EIF) is a user identifiable group of

logically related data or control information referenced by the application, but maintained within the boundary of another application

• The primary intent of an EIF is to hold data referenced through
• ne or more elementary processes within the application of the

application counted; this means an EIF counted for the application must be an ILF in another application

External Interface Files

Step 3: Data

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• To identify EIFs, look for groups of data or control information that

satisfy the definition of an EIF

• All of the following counting rules must apply for the information to be

counted as an EIF:

• The group of data or control information is logical and user

identifiable

• The group of data is referenced by, and external to, the application

being counted

• The group of data is not maintained by the application being

counted

• The group of data is maintained in an ILF of another application

Step 3: Data

EIF Identification Rules

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EIF Examples

• Count as External Interface Files
• Reference data or edit criteria obtained or read from ILFs

maintained by other applications

• Information not maintained within counted application, but

required to produce outputs/inquiries Step 3: Data

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The primary difference between an internal logical file (ILF) and an external interface file (EIF) is that an EIF is not maintained by the application being counted, while an ILF is.

ILF/EIF Difference

Step 3: Data

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Assign each identified ILF and EIF a functional complexity based on the number of data element types (DETs) and record element types (RETs) associated with the ILF or EIF, within that application

INTERNAL LOGICAL OR EXTERNAL INTERFACE FILES:

Record Element Types

Data Elements 1­19 20­50 51+ <2 Low 2­5 Average High >5 Low Low Average High Average High

(Data SubGroups) (Sum of all fields

• f all subgroups
• f the logical data

grouping)

Step 3: Data

ILF/EIF Complexity Matrix

Step 3: Data

ILF L = 7 A = 10 H = 15 EIF L = 5 A = 7 H = 10

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INTERNAL LOGICAL OR EXTERNAL INTERFACE FILES:

Record Element Types

Data Elements 1­19 20­50 51+ <2 Low 2­5 Average High >5 Low Low Average High Average High

(Data SubGroups) ­ 1 (Sum of all fields

• f all subgroups
• f the logical data

grouping) ­ 7

Step 3: Data

ILF L = 7 A = 10 H = 15 EIF L = 5 A = 7 H = 10

Internal Logical File Example

Entity Element Length INSTRUCTOR Name 30 Address 50 City 30 State 20 Zip 9 Telephone 10 Course Number 5

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Transaction Functions

• Transactional functions represent the functionality provided to the user

for the processing of data by an application

• Transactional functions are defined by their elementary process and

primary intent as follows:

• For the Elementary Processes where the Primary Intent is to

maintain an ILF or to alter the behavior of the system:

• External Inputs (EIs)
• For the Elementary Processes where the Primary Intent is to present

information to the user and that perform calculations, derive data, update an ILF or alter the behavior of the system:

• External Outputs (EOs)
• For the Elementary Processes where the Primary Intent is to present

information to the user and that do not perform calculations, derive data, update an ILF or alter the behavior of the system

• External Inquiries (EQs)

Step 4: Transactions

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Example of Functions (EI, EO, EQ)

Step 4: Transactions

Function EI EO EQ Provide a screen to add an instructor to the database or change instructor information x Provide a selection list of all instructors in the data base x Provide a report of instructors by course number with summary data x

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External Inputs

• An external input is an elementary process that processes data or

control information that comes from outside the application’s boundary

• The primary intent of an EI is to maintain one or more ILFs and/or

to alter the behavior of the system Step 4: External Input

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EI Identification Rules

All of the following counting rules must apply for data being processed to be counted as an external input:

• The data or control information is received from outside the

application boundary

• At least one ILF is maintained if the data entering the boundary is not

control information that alters the behavior of the system

• For the identified process, one of the three statements must apply:
• Processing logic is unique from processing logic performed by
• ther EIs for the application
• The set of data elements identified are different from the sets

identified for other EIs in the application

• The ILFs or EIFs referenced are different from the files

referenced by the other EIs in the application

Step 4: External Input

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EI Examples

Count as External Input

• Transactional data
• Screen or batch input
• Messages from other applications
• Control Information
• User functions
• Physical data which initiates processing

Examples that are not External Inputs

• Menu screens
• Logon screens
• Navigation

Step 4: External Input

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Complexity for External Inputs is based on the number of logical groups (FTRs) and fields (DETs) for the EI

Guideline: When estimating a FP count, use average unless High is obvious <2 2 >2

Low Average High Low Low Average High Average High

EXTERNAL INPUT: File Types Data Elements Referenced 1­4 5­15 16+ (Data Functions) (Fields)

EI Complexity Matrix

Step 4: External Input

EI L = 3 A = 4 H = 6

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• An external output (EO) is an elementary process that sends data
• r control information outside the application’s boundary
• The primary intent of an external output is to present information

to a user through the processing logic other than or in addition to the retrieval of data or control information

• The processing logic must contain at least one mathematical

formula or calculation, create derived data, maintain one or more ILFs and/or alter the behavior of the system Step 4: External Outputs

External Outputs

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All of the following counting rules must apply for the elementary process to be counted as an external output:

• Sends data or control information external to the application’s

boundary

• For the identified process, one of the three statements must apply:
• Processing logic is unique from the processing logic performed

by other EOs for the application

• The set of data elements identified are different from other EOs

in the application

• The ILFs or EIFs referenced are different from files referenced

by other EOs in the application

EO Identification Rules

Step 4: External Outputs

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In addition, one of the following rules must apply:

• The processing logic contains at least one mathematical

formula or calculation

• Derived data is created
• The processing logic maintains at least one ILF
• The processing logic alters the behavior of the system

Step 4: External Outputs

EO Identification Rules

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External Output Examples

Count as External Output

• Data transfers to other applications with calculations
• Reports with calculations
• On­line reports with calculated information
• Derived data displayed on a screen
• Message/file sent to another system, that includes an update (send a check

for payment, and update an ILF that the check has been processed)

Step 4: External Outputs

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Complexity is based on the number of FTRs/DETs for the EO

File Types Data Elements Referenced 1­5 6­19 20+ <2 2 or 3 >3

Low Average High Low Low Average High Average High

EXTERNAL OUTPUT: (Data Groups) (Fields)

EO Complexity Matrix

Step 4: External Outputs

EO L = 4 A = 5 H = 7

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• An external inquiry (EQ) is an elementary process that sends

data or control information outside the application boundary

• The primary intent of an external inquiry is to present information

to the user through the retrieval of data or control information

• The processing logic contains no mathematical formula or

calculation, and creates no derived data

• No ILF is maintained during the processing, nor is the behavior of

the system altered Step 4: External Inquiries

External Inquiries

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All of the following must apply:

• Sends data or control information external to the application’s

boundary

• For the identified process, one of the three statements must

apply:

• Processing logic is different from the processing logic

performed by other EQs for the application

• The set of data elements identified are different from other

EQs in the application

• The ILFs or EIFs referenced are different from files

referenced by other EQs in the application

Step 4: External Inquiries

EQ Identification Rules

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• In addition, all of the following rules must apply:
• The processing logic retrieves data or control information from
• ne or more ILFs or EIFs
• The processing logic does not contain mathematical formula
• r calculation
• The processing logic does not create derived data
• The processing logic does not alter the behavior of the system
• The processing logic does not maintain an ILF

Step 4: External Inquiries

EQ Identification Rules

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External Inquiry Examples

• Count as an External Inquiry
• User functions such as view, lookup, display, browse, drop down
• Logon screens that provide application specific security
• Help ­ each level
• Output that contains no calculated, derived data

Step 4: External Inquiries

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Complexity is based on the number of FTRs/DETs for the EQ

EXTERNAL INQUIRY: File Types Data Elements Referenced 1­5 6­19 20+ 1 2 or 3 >3

Low Average High Low Low Average High Average High

(Fields) (Data Groups)

Step 4: External Inquiries

EQ Complexity Matrix

Step 4: External Inquiries

EQ L = 3 A = 4 H = 6

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Step 4: Trans­ actions

Summary Of Processing Logic (EI, EO, EQ)

Step 4: Transactions

PROCESSING LOGIC EI EO EQ Validations are performed C C C Mathematical formulae or calculations are performed C M* N Equivalent values are converted C C C Data is filtered and selected using specified criteria to compare multiple sets of data C C C Conditions are analyzed to determine which are applicable C C C At least one ILF is updated M* M* N At least one ILF or EIF is referenced C C M Data or control information is retrieved C C M Derived data is created C M* N Behavior of the system is altered M* M* N Prepare and present information outside the boundary C M M Capability to accept data or control information that enters the application boundary M C C Resorting or rearranging of data C C C

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Summary Of Processing Logic (EI, EO, EQ)

Legend: – M it is mandatory that the function type perform the type of processing logic – M* it is mandatory that the function perform at least one of these (M*) forms of processing logic – C the function can perform the form of processing logic but it is not mandatory – N the function can not perform the form of processing logic

Step 4: Transactions

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Functionality requested by the user may be organized into logical parts that match the five function point components

External Interface File

USER ADD, CHG INVOICES PAYMENTS VENDOR INVOICES

ACCOUNTS PAYABLE

USER PAYMENTS USER PAYMENT STATUS USER PAID INVOICES PURCHASE ORDER INFO

PURCHASE ORDER SYSTEM

External Inputs External Input External Inquiry External Output Internal Logical Files

Managing Requirements

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Data Communication On­Line Update Distributed Data or Processing Complex Processing Performance Objectives Reusability Heavily Used Configuration Conversion & Install Ease Transaction Rate Operational Ease On­Line Data Entry Multiple­Site Use End­User Efficiency Facilitate Change

Step 5: Determine VAF

General System Characteristics

Step 5: Determine VAF

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Step 5: Determine VAF

• The value adjustment factor looks at 14 general system

characteristics.

• Each characteristic is given a value from 1 to 5
• Once all 14 GSCs have been evaluated, the

VAF is computed: Σ(DI) = TDI (TDI * .01) + .65 = VAF

• Effect is to adjust the count by + or – 35%

Value Adjustment Factor (VAF)

Step 5: Determine VAF

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General System Characteristic Guidelines

• Each guideline contains:
• A definition of the GSC
• Rules for determining the score
• If the rule needs further clarification, hints have been

provided to help apply the rules consistently across all platforms.

• Hints are not intended to cover all situations but are

meant to provide additional guidance in determining the appropriate score Step 5: Determine VAF Each of the following general system characteristic descriptions includes guidelines to determine the degree of influence.

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Formulas

• Total Degree of Influence (TDI) = Sum of DIs from all 14 GSCs
• Value Adjustment Factor (VAF) = (.65 + (.01 x TDI))
• Adjusted Function Points = Unadjusted FP x VAF
• NOTE: There are different algorithms for:
• Development
• Enhancement
• Original Application
• Revised Application Counts

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Development Project Calculation

The calculation consists of three components of functionality:

• Application functionality
• functions used after software installation to satisfy the
• ngoing business needs of the user
• Conversion functionality
• functions provided to convert data and/or provide other

user­specified conversion requirements, such as special conversion reports

• Value adjustment factor
• determined by using the 14 general system characteristics

to rate the application complexity

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Development Count

The following formula is used to calculate the development project function point count:

DFP = (UFP + CFP) * VAF Where DFP ­ development project function point count UFP ­ unadjusted function point count CFP ­ function points added by the conversion unadjusted function point count VAF ­ value adjustment factor After the software is installed, the application function point count is calculated using components of the development project function point count

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Application Count – Initial Count

The following formula is used to calculate initial function point counts for an application; the user is receiving functionality; there are no changes to existing functionality or deletions of unneeded functionality; the application function point count does not include conversion requirements: AFP = ADD * VAF Where AFP ­ initial application function point count ADD ­ unadjusted function point count of functions installed VAF ­ value adjustment factor of the application

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Enhancement Project Calculation

The calculation consists of three components of functionality:

• Application functionality ­ consists of:
• Function points identified from functionality added by

enhancements

• Function points counted because existing functionality is

changed during the project

• Function points counted for functionality deleted during the

project

• Conversion functionality ­ consists of function points delivered

because of any conversion requirements by the user

• Value adjustment factor ­ two adjustment factors include:
• adjustment factor before enhancement project begins
• adjustment factor after enhancement project completes

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Enhancement Count

The following formula is used to calculate the enhancement project function point count:

EFP = [(ADD + CHGA + CFP) * VAFA] + (DEL * VAFB) Where EFP ­ enhancement project function point count ADD ­ unadjusted function point count of added functions CHGA ­ unadjusted count of functions modified; reflects functions after modification CFP ­ function point count added by conversion VAFA ­ value adjustment factor of the application after the enhancement DEL ­ unadjusted count of functions deleted VAFB ­ value adjustment factor of application before the enhancement

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• Added (new) functionality increases the size of the application
• Changed functionality increases, decreases, or has no effect
• Deleted functionality decreases the size
• Changes to the value adjustment factor adds, subtracts, or has

no effect on the count

• Conversion functionality does not affect the count; any

conversion functionality associated with an enhancement project is not included in the application count

Application Calculation

When an enhancement project is installed, the existing count must be updated to reflect modifications; the functionality for the application can be altered in one or more ways :

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References

For more information:

• David Consulting Group
• www.davidconsultinggroup.com
• International Software Benchmarking Standards Group
• www.isbsg.org.au
• International Function Point Users Group
• www.ifpug.org
• Software Engineering Institute, Project Sizing & Estimating
• www.cmu.sei.edu

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Questions?