Functional Size of Real-Time
Software: Overview of Field Tests
Serge Oligny, Alain Abran, Jean-Marc Desharnais,
Pam Morris Presented at
13th International Forum on COCOMO and Software Cost Modeling Los Angeles, CA
k 1 .
4,
o
Context
o
Real-Time Software Limitations of
FPA
o
Full Function Points Core Concepts
. . . <
. -
o
Initial
Test
Results
o
Recognition from ISBSG
. ,5.
o
Additional Field Tests
.:'
Context...
IFPUG's Function Points (FPA,
v.
4.0):
O Designed and refined for the characteristics of business applications type of software,
O Measures software delivered to external human business users,
Context...
o
Since 1986, FPA has been criticized as not being applicable to all types of software:11
A problem with the function point approach is that it assumes a limited band of application types: typically, large file- based
systems produced by agencies such as banks
...
, and is unable to cope with hybrid systems such as a stock control system with a heavy communication component. 'qo
Although the FPA measurement method generates results in such cases, these results do notconstitute an adequate size measurement.
':
lnce D.C., History and industrial applications, in Fenton N.E., Software Metrics: A Rigorous Approach, Chapman & Hall, 199 1, p. 283o
Real-Time systems (RTS) are examples of software that differs from 'business application" software,o
RTS are thus examples of software for which FPA isnot an adequate FSM.
...
Is
the functional size of real-time systems isContext.,.
o
RTS represent approximately 5O0/0 of the softwarein production in the United-States,
o
RTS contributes t o the software portfolio; it has t o be purchased, customized, documented, maintained, etc.o
Supported RTS should be included in the assignment scope when calculating support productivity,development and maintenance budgets, etc.
o
RTS delivered as part of a project will need effortassigned t o it and should be included in total project 8
size for accurate estimates. 1.
Real-Time software limitations
of
FPA...
So, what are the limitations of FPA when applied to RTS ?o
Value Adjustment Factor does not adequately cover the impact on productivity for RTS,o DATA LIMITATIONS:
as opposed to "external business application software", the primary role of RTS is NOT to maintain and report stored data
(primary role is to process input data for immediate response or output ),
in RTS, most of the data input is not stored permanently, RTS data is simple and typically includes
J historical logs of input values
4 threshold values
Real-Time software limitations of
FPA...
o
PROCESS LIMITATIONS:O RTS processes contain many internal sub processes where
functionality is n o t represented by data crossing the external boundary,
O RTS processes display an exponential difference in functional
size that cannot be recognized by the twofold increment in
allocated FPA,
O RTS processes do not usually display a predominant input or
output characteristic and thus cannot easily and consistently
Full
Function
Points core concepts
...
o
By design, the FFP measurement method:adopts a FULL functional perspective spanning more than the functionality perceived by RTS's human users; it includes
functionality interacting with other software and phvsical
devices,
does not impose a maximum size t o a process; the size of a
process is the SUM of the size of its individual sub processes,
does not assign a predominant functional role (input or output) t o each process,
Full Function Points core concepts...
.
0
!
READ-ONLY
DATA GROUP UPDATED i
DATAGROUP i
...
Full
Function Points core concepts
...
:; :
$
;: ? THEREFORE, FFP: b
o
...
can be used t o measure the functional size o f any type o f software, including RTS,O
...
offers a result that is not restricted t o a twofoldmaximum range for each identified process,
O
...
enables processes t o be consistently sized when they do n o t display a predominant input o r outputcharacteristic,
O
...
can be applied t o processes whose functionality does n o t pass data externally,I
r A O
...
enables measurement o f simple groups of data.Initial
test results
...
o
First set of field tests (1997):o
conducted bythe research team,o
3 RTS or embedded software products measured,o
2 industrial partners in USA and Canada,o
GOAL: compare IFPUG 4.0 FPA with FFPo
RESULTS:FFP results close to FPA when processes contained small number of sub processes,
FFP results yield larger size measure when processes contained large numbers of sub processes.
Initial test results.
..
o
Second set of field tests (1997):o
conducted without ass'stance I from the research team,o
RT operational software products,o
1 industrial partner in Japan,o
GOAL: evaluate FFP for relevance and usabilityo
RESULTS:J concepts and procedures are clear and easy to
understand, usable without assistance from measurement specialists,
J FFP functional coverage established at 97% of
Recognition from
ISBSG...
o
ISBSG: International Software Benchmarking StandardsGroup
Maintains a repository of measured software products and projects,
Currently over 500 historical software projects available, Rigorous entry and validation methodology,
Functional size measure MANDATORY for acceptance of
Recognition from ISBSG...
o
FFP recently recognized as a valid FSM by ISBSG FFP accepted based on list of rigorous criteria,Interim status: accept project where software measured with FFP,
After submission of a minimum number of FFP measured software products, ISBSG will modify entry and validation software.
Additional set of field tests...
I
I @ CONTEXT:
3 4 industrial partners
3 in North-America,
J 1 in Asia (not Japan).
o
10 software products4 never measured before with FFP,
4 8 products related to the telecom. industry,
J 1 product related to operation of a power utility org.,
1 product related to the military sector.
o
All software products measured by thesame individual4 CFPS,
Additional
set
of field
tests...
lSt GOAL: further compare IFPUG 4.0 FPA and FFP
RESULTS:
Product Type FPA size FFP size Difference Diff.as O/O
Size is similar when measuring typical MIS software products
Additional set
of
field tests...
lst GOAL: further compare IFPUG 4.0 FPA and FFP
Product Type FPA size FFP size Difference Diff.as O/O
1
Real-Time
Additional
set
of
field tests...
lSt GOAL: further compare IFPUG 4.0 FPA and FFP
RESULTS:
(
Product Type FPA size FFP size Difference Diff.as O/oA Real-Time 210 794
584
74%
B Real-Time
115
183 68 3 7 */oC Real-Time 0 2 604 2 604 10Oo/o
D Real-Time 43 318 275 8 6 O/O
I :;. ' ; , ! , . , , . i i A . ., . , . , 3 2 7 , '3 '.' /I ' ; r
F MIS (batch)
272
676 404 60 O/O/ ;!..y. t > 1 ': : .;' , i,',
Larger functional size for software products with
numerous R-T processes (A through D); even for
MIS
Additional set of field tests...
2nd GOAL: explore magnitude of key economic values
RESULTS: These 3 software products are all R-T software
Product Size Effort Duration Unit effort Sched. del.
(FFp) (ph) (mth) (ph/FFP) Rate (FFP/mth)
Until further data is available to allow statistically significant analysis, these should be interpreted as "order of magnitude" figures.
Conclusion..
.
o
FIELD TEST RESULTS SUMMARY:o
1st set of field testJ FFP functional size results reflect the varying functional size typically found in RTS processes,
o
2nd set of field testFFP concepts and procedures can be applied without the help of an FSM specialist,
J From a practitioner's point of view, FFP offers a high
22
Conclusion...
o
FIELD TEST RESULTS SUMMARY:o
3rd set of field testFurther illustrates the difference in functional size obtained from FPA and FFP when both methods are applied to the same software products,
Provides first indications on order of magnitude for key economic ratios related to FFP.
I
1 I
Acknowledgments
o
The Software Engineering Management
Research Laboratory of the Universit6
du
Qubbec
5
Montreal is supported through
a
partnership with
Bell
Canada.
o
Additional funding is provided by the
Government of
Canada.
