function point analysis: a quick and easy primer · itmpi005 click to edit master title 1. david...

T11 Concurrent Session Thursday 06/12/2008 1:00 PM – 2:30 PM

Function Point Analysis: A Quick and Easy Primer

Presented by:

David Garmus & David Herron The David Consulting Group

Presented at: Better Software Conference & EXPO

June 9 – 12 2008: Las Vegas, NV, USA

330 Corporate Way, Suite 300, Orange Park, FL 32043 888-268-8770 904-278-0524 [email protected] www.sqe.com

David Garmus David Garmus is a founder of The David Consulting Group (an SEI CMMI® Approved Transition Partner) and supports software development organizations in achieving software excellence with a metric-centered approach. David is an acknowledged authority in the sizing, measurement, and estimation of software application development. He is a past president of the International Function Point Users Group (IFPUG) and a member of their Counting Practices Committee. David has spoken at numerous conferences and written many articles and several books.

David Herron David Herron is an acknowledged authority in the use of metrics to monitor the impact of Information Technology (IT) on the business and on the advancement of IT organizations to higher levels of software process maturity. He is a noted author and lecturer and has addressed audiences throughout the US and Europe on performance measurement, software process improvement, and outsourcing governance. With David Garmus, David Herron has co-authored two books on functional measurement. David Herron’s current engagements include senior-level consulting and coaching on matters relating to organizational change management, team, and individual mentoring.

http://www.davidconsulting.com/

ITMPI005

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David Garmus and David Herron

June 2008Better Software Conference

Function Point Analysis: A Quick and Easy Primer

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Topics of Discussion

Function Point Analysis, Uses and Benefits

• Objectives of Function Point Analysis• Benefits of Function Point Analysis• A High Level View• 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 thefunctionality 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 organization 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 thesecomponents in the next module

Overview

FP Evaluates These Components

External Input

External Inquiry External

Output

InternalLogical

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

4. Count the transactional functions to determine their contribution to the unadjusted function point count

5. Determine the value adjustment factor - 14 General System Characteristics

6. Calculate adjusted function point count

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

ExternalInput

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

Data Functions

Step 3: Data

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

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• To identify ILFs, look for groups of data orcontrol information that satisfy the definitionof an ILF

• All of the following counting rules mustapply for the information to be counted asan 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

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

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 one 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

• System 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 OREXTERNAL INTERFACE FILES:

Record Element Types

Data Elements1-19 20-50 51+

<2 Low2-5 Average High>5

LowLow Average

HighAverage High

(Data SubGroups)

(Sum of all fieldsof all subgroupsof the logical datagrouping)

ILF/EIF Complexity Matrix

Step 3: Data

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“Instructor Data”Entity Element LengthINSTRUCTOR

Name 30Last NameFirst NameMiddle Init

Address 50City 30State 20Zip 9Telephone 10

COURSES TAUGHTInstructor Name 30

Last NameFirst NameMiddle Init

Course Name 20Course Number 8

CoursesTaught

Dependenton

Instructor

Internal Logical File Example

Step 3: Data

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Solution

Sample Counting Form

Step 3: Data

DescriptionILF/EIF

EI/EO/ EQRET/ DET

FTR Complexity

INSTRUCTOR DATA ILF 2 8 Low

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The Customer Address File is used to print the addresses on the bills. No Billing System files are updated with this data.

Completed Orders File updates the Billing Master and cause the bills to be processed.

CustomerAddress File

CompletedOrders File

BILLING SYSTEM

Billing Master

External Interface File Example

Step 3: Data

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Solution

Step 3: Data

DescriptionILF/EIF

EI/EO/ EQRET/ FTR

DET Complexity

CUSTOMER ADDRESS FILEBILLING MASTER FILECOMPLETED ORDERS FILE

EIFILF─

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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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Legend:PI: primary intent of the transaction functionF: function of the transaction function, but is not the primary intent

and is sometimes presentN/A: the function is not allowed by the transaction function

Summary of Functions (EI, EO, EQ)

Step 4: Transactions

Function EI EO EQAlter the behavior of the system PI F N/A

Maintain one or more ILF PI F N/A

Present information to the user F PI PI

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Summary Of Processing Logic (EI, EO, EQ)

Step 4: TransactionsPROCESSING 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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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 other 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


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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

Don’t count as External Input• Reference data (EIFs)• Input side of EQ or EO• Menu screens• Logon screens• Multiple methods of invoking similar logic• Navigation


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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 HighLow

Low Average

HighAverage High

EXTERNAL INPUT:

File Types Data ElementsReferenced 1-4 5-15 16+

(Data Groups)(Fields)

EI Complexity Matrix


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Course Registration Screen

NAME ____________________ START DATE (PK)______

SSN (PK)_____________________

COURSE # (PK)________________

COURSE TITLE ____________

LOCATION ________________ ACTION (A, C OR D)____

(Both Error and Confirmation Messages Occur)

STUDENT and COURSE are updated/referenced.


External Input Example

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Solution


DescriptionILF/EIF EI/EO/

EQ

RET/ FTR

DET Complexity

REGISTRATION FORM (Add)REGISTRATION FORM (Change) REGISTRATION FORM (Delete)

EIEIEI

222

885

AvgAvgAvg

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• An external output (EO) is an elementary process that sends data or 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


• 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


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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


EO Identification Rules

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External Output Examples

Count as External Output• Data transfers to other applications with calculations• Reports with calculations• On-line 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)• Note: Summary fields on a report are not counted as a separate EO; these

computed fields are DETs within the same EO

Don’t count as External Output• Reports without other processing (calculations, update, etc.)• Identical reports/unique data values• Resorting or rearrangement of a set of data without other processing logic


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


<2 2 or 3

>3

Low

Average HighLow

Low Average

HighAverage High

EXTERNAL OUTPUT:

(Data Groups)(Fields)

EO Complexity Matrix


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Course Roster Report

Course Name xxxx Course Number xxxCourse Location xxxxx Instructor Name xxxxxxx

Student Name Address SSNxxxxxxx, xxxx x. xxxxxxxxxxxx nnn-nn-nnnn

xxxxxxxxxxxx

xxxxxxx, xxxx x. xxxxxxxxxxxx nnn-nn-nnnnxxxxxxxxxxxx

TOTAL NUMBER OF STUDENTS nnnn

STUDENT and COURSE are referenced.


External Output Example

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Solution


DescriptionILF/EIF

EI/EO/ EQRET/ FTR DET Complexity

COURSE ROSTER EO 2 8 Avg

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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


• 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


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 one or more ILFs or EIFs

• The processing logic does not contain mathematical formula or 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


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

• Don’t count as External Inquiry• Multiple methods of invoking the same inquiry logic• Inquiries that can be accessed from multiple areas/screens of an application

(count once)• Logon screens that do not provide security• Derived data vs. retrieval of data• Resorting or rearrangement of the same set of data without other processing

logic


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

EXTERNAL INQUIRY:


1 2 or 3

>3

Low

Average HighLow

Low Average

HighAverage High

(Fields)(Data Groups)

EQ Complexity Matrix


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Restaurant Selection

S TypeItalian

x MexicanBistro

Restaurant Selection

Name: TACO BELLLocation: EVERY CORNERGolden Spoon Rating -2Price Range CHEAPReservations Never Needed

Screen1 - input Screen 2 - output



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College Credits Report

Student Course Number Course Date Creditsxxxxxxxxxxx, xxx nnnnnnn nn/nn/nnnn nnnnxxxxxxxxxxx, xxx nnnnnnn nn/nn/nnnn nnnnxxxxxxxxxxx, xxx nnnnnnn nn/nn/nnnn nnnnxxxxxxxxxxx, xxx nnnnnnn nn/nn/nnnn nnnnxxxxxxxxxxx, xxx nnnnnnn nn/nn/nnnn nnnn



(Info is retrieved from Course ILF)

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Solution


DescriptionILF/EIF EI/EO/

EQ

RET/ FTR

DET Complexity

RESTAURANT SELECTIONCOLLEGE CREDITS REPORT

EQEQ

11

74

LowLow

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

External Interface File

USERADD, CHGINVOICES PAYMENTS

VENDOR

INVOICES

ACCOUNTS PAYABLE

USER

PAYMENTS

USER

PAYMENTSTATUS

USER

PAIDINVOICES

PURCHASEORDER INFO

PURCHASEORDERSYSTEMExternal Inputs

External Input

External Inquiry

External Output

Internal Logical Files

Managing Requirements

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Data Communication On-Line Update

Distributed Data or Processing Complex Processing

Performance Objectives Reusability

Heavily Used Configuration Conversion & Install Ease

Transaction Rate Operational Ease

On-Line Data Entry Multiple-Site Use

End-User Efficiency Facilitate Change

General System Characteristics

Step 5: Determine VAF

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• The value adjustment factor looks at 14 general system characteristics.

• Each characteristic is given a value

• Once all 14 GSCs have been evaluated, the VAF is computed:

Σ(DI) = TDI(TDI * .01) + .65 = VAF

Value Adjustment Factor (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


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

Step 6: Final Calculation

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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 organization by counting functions that specifically match requirements

• A tool to size or evaluate purchased application packages

Just to Summarize…

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References

For more information:

• The 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

http://www.davidconsultinggroup.com/

http://www.isbsg.org.au/

http://www.ifpug.org/

http://www.cmu.sei.edu/

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