iwsm2014 an evaluation of simple function point as a replacement of ifpug function point (luigi...

Università degli Studidell’Insubria

An Evaluation of Simple Function Pointas a Replacement of IFPUG Function Point

Luigi Lavazza

Dipartimento di Scienze Teoriche e Applicate

Università degli Studi dell'Insubria - Varese

Roberto Meli

SiFPA

IWSM 2014

Contents

Research motivations

Simple Function Point: definition

FP vs. SiFP as size measures: statistical analysis

FP vs. SiFP as effort predictors: statistical analysis

Expected advantages in using SiFP

Rotterdam, October 20142

Two crucial and intriguing questions …

Why should anybody abandon the IFPUG FSMM ?

Why should anybody need a brand new FSMM just right now ?

Rotterdam, October 2014IWSM 2014 3

Why should anybody abandon the IFPUG FSMM ?

Because you can get the same results with less effort, time and costSetup of the measurement system

– training, individual study, certification, field experience, guidelines, ...

Execution of the measures– measurement productivity

Documentation of the measures– registered details

Measure’s verification & validation– audit, investigation, contradictory, litigation, ...


Why should anybody need a brand new FSMM just right now ?

Because the current most popular alternative FSMMs present the same problems of the IFPUG method: too much details and complexity.

Because the market is now declining and the organizations need to cut off all non strictly crucial costs.

Because the "agile movement" is conquering considerable attention and business spaces and actual FSMMs are not perceived as agile at all.

Because, despite everything, you can not loose the investments made over the years on IFPUG measures and no alternative FSMM is highly convertible with IFPUG.


What’s the need then ?

Today’s software market requires

fast, agile, effective functional size measurement methods with low impact on production processes,

which require not too specialized skills, that are reliable in results, not dependent on expert’s opinions and technology.

The resulting measures should be adequately correlated to effort, cost, duration of a new development or functional enhancement software project.

Current Functional Size Measurement Methods (FSMM) are only partially compliant with these needs.


IWSM 2014

IFPUG Function Point: the software model

SW application functional specifications

Logical file Transaction

Data Element Type

Record Element Type

FTR

0..*

I/O

1..*

Allan J. Albrecht


Primary intent

7

IWSM 2014 8

Simple Function Point: the software model



Data Element Type

Record Element Type

FTR

0..*

I/O

1..*


UGDG UGEP


Primary intent

UGEP

"An atomic set of functional user requirements conceived for processing purposes. It refers to an informational or operational goal considered significant and unitary by the user and includes all automated, mandatory and optional activities needed to meet the goal. After an UGEP is concluded, the MSA to which it belongs must be in a logically consistent state."

Unspecified Generic Elementary Process

IWSM 2014 9 Rotterdam, October 2014

UGDG

Fundamental data group

Auxiliary or non functional data group

Only the first category (the fundamental data group) meets user functional requirements and can therefore be identified as a UGDG.

Role

Unspecified Generic Data Group

Employee

"An atomic set of user requirements having a storage purpose. It refers to a single logical data set of interest to the user, for which information must be kept persistently."


SiFP Definition process

With the IFPUG measurement, weights are computed for each data and transaction function, by analyzing its details.

With the SiFP measurement, weights are fixed Weights were derived from the analysis of the ISBSG dataset in order

to maximize convertibility

SiFP = 4.6 #UGEP + 7 #UGDG


The number of elementary processes, without considering the primary intent

The number of logical data files, without considering if they are internal or external

Measurement Procedure


Measurement process: FP vs. SiFP

IWSM 2014 13

Gather the available documentation

Identify application boundaries

Determine the measurement goal and scope

Locate Elementary Processes and Logical Data Files

Identify transactions’ primary intents, internal/external files, RET, DET, FTR and

determine complexity

Calculate the functional size

Document and present the measurement

[SiFP]

[IFPUG]

5%

25%

60%

10%


Activities Cost fraction

5%

25%

60%

10%

Software Architecture

Technical Component Layer

(Technical Generalized Services)

Software

Layers

App 1Application Layer App 2 App ‘n’

Operating System Layer (File System)

Database Management System Layer

DBMS 1 DBMS 2

Application Component Layer

(Business Generalized Services)

Enterprise System


Where can you find reference manuals ?

In the public

domain

for free !

www.sifpa.org


Just one final highlight

SiFP is not an IFPUG approximation technique like Early & Quick FP, Indicative FP, extrapolative FP and many others based on average scores…

SiFP is a FSMM which is (actually) higlhy “convertible” with IFPUG method and it gives “precise”, not approximate, measurements of software functional requirements.


Research questions

How well are IFPUG FP and SiFP correlated?

How large is the difference of FP and SiFP size measures for the same software application?

To answer these questions, we analyzedThe ISBSG dataset (also used for the definition of the

BFC weights)A second business dataset


Plot FP vs. SiFP (ISBSG)

IWSM 2014 18


Regression lines (ISBSG)

IWSM 2014 19

SiFP = 0.998 UFP

Without outliers

With outliers


% differences (ISBSG)

IWSM 2014 20

Including outliers!


Regression lines (ISBSG)

IWSM 2014 21

In practice 1 SiFP = 1 UFP.

But is this statistically correct?


SiFP = 0.998 UFP

Line SiFP = UFP in in the 95% confidence interval.

Plot FP vs. SiFP (validation dataset)

IWSM 2014 22


IWSM 2014 23

% differences (validation dataset)


What happens if we consider sw portfolios?

Till now, we have considered measures taken on the same application using the two FSMM.

What happens when we consider a portfolio of applications and we are interested into the global portfolio size difference which is affected by the compensations among positive differences and negative differences in the relation between IFPUG FP and SiFP ? This is the case of application asset evaluations or of broad procurement contracts.


25

Results from the entire ISBSG DB


Individual differences

UFP SiFP DELTA DELTA% ABS(DELTA%)somma 284.005,0 282.881,6 -1.123,4 -0,4%minimo 10,0 9,2 -735,0 -47,4% 0,0%media 370,8 369,3 -1,5 11,6%

mediana 215,5 216,4 0,0 9,9%massimo 3.886,0 3.468,2 485,4 41,4% 47,4%

SiFP-UFP portfolio size difference

-60%-50%-40%-30%-20%-10%

0%10%20%30%40%50%

0 1000 2000 3000 4000 5000

Distribuzione Delta%

IWSM 2014

Results from ISBSG DB (various portfolio sizes)

UFP SiFP DELTA DELTA% ABS(DELTA%)Minimo 10.002,00 9.378,60 -725,40 -7,18% 0,00%Media 10.235,56 10.212,62 -22,94 2,01%Mediana 10.193,50 10.184,40 -13,00 1,58%Massimo 10.769,00 11.030,40 553,80 5,43% 7,18%

UFP SiFP DELTA DELTA% ABS(DELTA%)Minimo 25.005,00 24.236,00 -1.061,00 -4,19% 0,01%Media 25.429,83 25.468,33 38,50 1,51%Mediana 25.257,50 25.427,50 -3,50 1,16%Massimo 27.039,00 27.252,20 1.375,20 5,31% 5,31%

UFP SiFP DELTA DELTA% ABS(DELTA%)Minimo 50.001,00 48.757,40 -1.247,60 -2,49% 0,02%Media 50.451,70 50.604,99 153,29 1,11%Mediana 50.264,00 50.549,50 228,90 0,98%Massimo 52.187,00 52.109,40 1.594,20 3,18% 3,18%


Portfoliosize

Learnability

180 professionals with no previous knowledge of FSMMGrouped in 75 teams3 hours SiFP training 30-45 minutes for measuring the case study (~270 SiFP)

Class Frequency % cumulative-35% 1 1,33%-27% 2 4,00%-18% 9 16,00%-10% 24 48,00%

-1% 14 66,67%7% 18 90,67%

16% 2 93,33%24% 3 97,33%

>24% 2 100,00%

-10%<x<+7% 75%-18%<x<+16% 89%


Another research questions

If we estimate development effort based on SiFP instead of IFPUG FP, the achieved accuracy is the same, better or worse?

To answer this question, We derived the (best) model of effort as a function of UFP size, via

OLS log-log regression using ISBSG data We derived the (best) model of effort as a function of SiFP size, via

OLS log-log regression using ISBSG data We estimated efforts using both models, and computed residuals

(i.e., actuals-estimates) We compared the residuals


The models of effort

As it could be expected, the models found were very similar:Effort = 2.9204 × UFP0.9074 Effort = 2.773 × SiFP0.92


0 500 1000 1500 2000 2500 3000 3500 4000 45000

1000

2000

3000

4000

5000

6000

UFP / effortSiFP / Effort

Functional Size (UFP / SiFP)

Eff

ort

(h

ou

rs)

IWSM 2014 30

Absolute relative residuals (ISBSG)


Neither Wilcoxon sign rank test not Mann-Whitney (Wilcoxon rank sum) test reject the hypothesis that absolute relative residuals are equal in the two cases.

A problem

We performed the analysis using the ISBSG dataset

In the ISBSG dataset there are many application such that the UFP and SiFP measures are very similar: in such cases, the effort estimates will also be very similar.

To overcome this problem, we repeated the analysis considering only the applications whose FP and SiFP measures are different by no less than 20%.


Applications having UFP and SiFP measures substantially different

IWSM 2014 32

We considered only the points out of this area


For instance, this application is about 2300 SiFP and over 3000 UFP

Results obtained considering only application with size measure difference ≥ 20%

IWSM 2014 33

Models

Effort =29.23 × UFP0.789 Effort = 17.22 × SiFP0.86

Adjusted R2 0.551 0.539

MMRE 56.8% 58.1%

MdMRE 41% 39.3%

Pred(25) 33.3% 40%

Error range [ -85% .. 247% ] [ -88% .. 269%]


Results are very similar!

Results obtained considering only application with size measure difference ≥ 20%


Neither Wilcoxon sign rank test not Mann-Whitney (Wilcoxon rank sum) test reject the hypothesis that residuals are equal in the two cases.

Residuals of effort estimates

So, according to statistical analysis …

SiFP and IFPUG measures are equivalent!


IWSM 2014 36

On the ability to explain development effort



Data Element Type

Record Element Type

FTR

0..*

I/O

1..*

R2 = 0.551


Logical file Transaction R2 = 0.539


IWSM 2014 37

On the ability to explain development effort

The performed analysis tell us that: To estimate the development effort, counting RET, DET, FTR, etc. is

of no use. In fact, SiFP do not count them, and get the same estimation

accuracy

Instead, we need models of this type:

Effort = f(S, p1, p2, …, pn)

S is the size, measured in FP or in SiFP

p1, p2, …, pn are parameters that characterize the software product (complexity, reliability, etc.) and the development process (develeopers’ capacity and experience, usage of tools and methodologies, etc.)


Conclusions

A new functional method based on just two BFC: Unspecified Generic Elementary Process (UGEP) Unspecified Generic Data Group (UGDG)

Totally compliant with IFPUG benchmarks It requires less details

2 to 5 times faster to measure Easy to learn and master Applicable by non specialists Less occasions for disagreement between clients and providers

1 SiFP =1 UFP Same development cost as IFPUG FP Conversion of historical data is immediate


Conclusions

By means of rigorous statistical analysis we were able to show that:The difference between UFP and SiFP measures is

generally small– Very small, when considering applications portfolios

For effort estimation, using SiFP instead of UFP does not cause the estimation accuracy to decrease

Conclusion: SiFP appear usable instead of UFP (and models based on UFP can be used with SiFP measures)

Anybody may test the model using his/her data with no additional effort provided that the number of EI, EO, EQ, ILF, EIF is known


iwsm2014 an evaluation of simple function point as a replacement of ifpug function point (luigi...

Software

ifpug measurement

sifp measurement

measurement goal

functional sizedocument

measurement process

measurement proceduregather

size measures

measurement system training