Information Technology Reference
In-Depth Information
Function Points and Other Metrics
The plethora of function point variants is not really helpful to eco-
nomic understanding. The rival claims among the function point
variants for being “more accurate” are also not helpful. Function
points in all flavors are counted using a complex set of rules, and
there are variances in counts even by certified counting person-
nel. There is no “cesium atom” or absolute standard against which
benchmark accuracy can be compared.
However, function points are the only available metric that
provides useful economic data and can successfully normalize res-
ults. The older
lines of code
metric penalizes modern programming
languages and makes requirements and design invisible. The
widely used
cost per defect
metric violates standard economic as-
sumptions and also penalizes quality, achieving the lowest cost per
defect for the buggiest software.
Other metrics such as story points for Agile projects are not
standardized and vary so widely from group to group that statistical
analysis is pointless.
Use-case points are more stable (although not standardized) but
are only good for projects that actually design software with use
cases. They have no value for cross-methodology comparisons.
Function points in all flavors are the best and most reliable met-
rics yet developed for software benchmarks and for software eco-
nomic studies. The ISBSG is a major source of data using function-
al metrics.
One caveat about functional metrics is that manual counting is
so slow and so expensive that functional metrics are seldom used
on systems larger than about 10,000 function points. Manual func-
tion point counting averages about 500 function points per day for
certified counters. The costs of manual function point counts range
between about $2.50 and $5.00 per function point counted.
Large systems in the 100,000 function point range (such as op-
erating systems, defense systems, and ERP packages) are almost
never counted with function points and therefore are not included
in the ISBSG repository.
Search WWH ::
Custom Search