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90 PART TWO MANAGING SOFTWARE PROJECTS

FIGURE 4.5 Weighting factor
Computing
function points Measurement parameter Count Simple Average Complex
Number of user inputs × 3 4 6 =
Number of user outputs × 4 5 7 =

Number of user inquiries × 3 4 6 =

Number of files × 7 10 15 =
Number of external interfaces × 5 7 10 =

Count total

the appropriate table location. Information domain values are defined in the follow-
ing manner: 5
Number of user inputs. Each user input that provides distinct application-
oriented data to the software is counted. Inputs should be distinguished from
inquiries, which are counted separately.
Number of user outputs. Each user output that provides application-
Function points are oriented information to the user is counted. In this context output refers to
derived from direct reports, screens, error messages, etc. Individual data items within a report
measures of the are not counted separately.
information domain.
Number of user inquiries. An inquiry is defined as an on-line input that
results in the generation of some immediate software response in the form of
an on-line output. Each distinct inquiry is counted.
Number of files. Each logical master file (i.e., a logical grouping of data that
may be one part of a large database or a separate file) is counted.
Number of external interfaces. All machine readable interfaces (e.g., data
files on storage media) that are used to transmit information to another sys-
tem are counted.

Once these data have been collected, a complexity value is associated with each
count. Organizations that use function point methods develop criteria for determin-
ing whether a particular entry is simple, average, or complex. Nonetheless, the deter-
mination of complexity is somewhat subjective.
To compute function points (FP), the following relationship is used:
FP = count total [0.65 + 0.01 ∑(F )] (4-1)
i
where count total is the sum of all FP entries obtained from Figure 4.5.

5 In actuality, the definition of information domain values and the manner in which they are
counted are a bit more complex. The interested reader should see [IFP94] for details.