Backfire Method

The Backfire Method is a means of estimating the count of SLOC that is equivalent to the adjusted function point count. Software Productivity Research, a firm lead by software metrics expert Capers Jones, has established “language multiplier” values for the major programming languages. The language multiplier gives the average number of SLOC per function point for that language. If the implementation language is chosen, one can estimate SLOC by multiplying the adjusted function point count by the language multiplier.

The Backfire Method is not part of the formal Function Point Analysis as defined by IFPUG. In COSMOS, however, the Backfire Method is used along with the Function Point Analysis, and is implemented in the Function Point Model.

Added, Changed, and Deleted Functionality

A software development project can basically do three things, separately or in combination:

• Functionality can be added – new functionality.(If the application does not already exist, this is all that can be done)

• Functionality can be changed – different functionality.

• Functionality can be deleted – removed functionality.

All three of these possibilities are reflected in IFPUG’s formula for the function points of a development project with software enhancement:

EFP = [ ( ADD + CHGA + CFP ) * VAFA ] + ( DEL * VAFB )

where:

EFP = Enhancement project function point count

ADD = Unadjusted function point count of added functionality

CHGA = Unadjusted function point count of changed functionality, after the project

CFP = Unadjusted function point count of conversion functionality

DEL = Unadjusted function point count of deleted functionality

VAFA = Value adjustment factor, after the project

VAFB = Value adjustment factor, before the project

If the project only includes new development – added functionality – the formula for the project function point count reduces to:

DFP = ( UFP + CFP ) * VAF

where:

DFP = Development project function point count

UFP = Unadjusted function point count of new functionality

CFP = Unadjusted function point count of conversion functionality

VAF = Value adjustment factor

In a COSMOS function point model (and project), only one VAF is computed. Because of this, COSMOS projects have one restriction: Deleted functionality cannot be included in the same project as added functionality and changed functionality.If application functionality must be deleted, that must be estimated as a separate project with its own general system characteristic settings (and VAF value). This is because in IFPUG’s formula for computing the function point of a development project, deleted function points are adjusted by the VAF of the applicationbeforethe project, notafter.

It is perfectly fine to include added functionality and changed functionality in the same COSMOS project.